Method of manufacturing semiconductor device

ABSTRACT

The present invention is characterized in that gettering is performed such that impurity regions to which a noble gas element is added are formed in a semiconductor film and the metallic element included in the semiconductor film is segregated into the impurity regions by laser annealing. Also, a reflector is provided under a substrate on which a semiconductor film is formed. When laser light transmitted through the semiconductor film substrate is irradiated from the front side of the substrate, the laser beam is reflected by the reflector and thus the laser light can be irradiated to the semiconductor film from the read side thereof. Laser light can be also irradiated to low concentration impurity regions overlapped with a portion the gate electrode. Thus, an effective energy density in the semiconductor film is increased to thereby effect recovery of crystallinity and activation of the impurity element.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a semiconductor device manufactured byincluding the step of annealing a semiconductor film using a laser beam(hereinafter referred to as laser annealing) and a manufacturing methodthereof. Note that the semiconductor device indicated here includes anelectrooptical device such as a liquid crystal display device or a lightemitting device and an electronic device including the electroopticaldevice as a part.

2. Description of the Related Art

A technique for performing laser annealing to a semiconductor filmformed on an insulating substrate made of glass or the like tocrystallize it or to improve crystallinity thereof is widely studied.Silicon is often used for the above semiconductor film.

Recently, in order to improve mass production efficiency, there isremarkable movement toward enlargement of a substrate such that thestandard substrate size used in production lines of newly constructedfactories is now becoming 600 mm×720 mm. It is difficult with acurrently available technique to process a synthetic quartz glasssubstrate into a substrate having such a large area. Even if that ispossible, it is considered that its price cannot be reduced to a levelpractical for industrial use. There is, for example, a glass substrateas a material capable of easily manufacturing a large area substrate.The glass substrate has an advantage such as low cost and easiness ofmanufacturing the large area substrate, as compared with the syntheticquartz class substrate frequently used in the prior art. Also, a laseris preferably used for crystallization because the melting point of theglass substrate is low. The laser can apply high energy to only asemiconductor film without largely increasing a temperature of thesubstrate.

There is a substrate called, for example, Corning 7059 as the glasssubstrate. Corning 7059 is quite inexpensive, has high processability,and can be easily enlarged in size. However, the distortion pointtemperature of Corning 7059 is 593° C. and a problem is caused in thecase of heating at 600° C. or higher. Also, there is Corning 1737 havinga relatively high distortion point temperature as one of glasssubstrates. The distortion point temperature of Corning 1737 is 667° C.and higher than that of Corning, 7059. Even when an amorphoussemiconductor film is formed on the Corning 1737 substrate and it isleft at 600° C. for 20 hours, a deformation of the substrate such as toaffect a manufacturing process was not observed. However, the heatingtime of 20 hours is too long for a mass production process. Also, it ispreferable that the heating temperature of 600° C. be as lower aspossible in view of a cost.

In order to solve such problems, a new crystallization method isdevised. This method is described in details in Japanese PatentApplication Laid-open No. Hei 7-183540. Here, this method will bebriefly described. First, a trace amount of metallic element such asnickel, palladium, or lead is added to an amorphous semiconductor film.The addition method is preferably performed using plasma processingmethod, an evaporation method, an ion implantation method, a sputteringmethod, a solution coating method, or the like. After the aboveaddition, for example, when the amorphous silicon film is left in anitrogen atmosphere at 550° C. for 4 hours, a crystalline semiconductorfilm having a preferable characteristic is obtained. Heatingtemperature, heating time, and the like, which are suitable forcrystallization are dependent on an addition amount of metallic elementand a state of the amorphous semiconductor film.

However, according to the above technique, there is a problem in thatthe metallic element used for promoting crystallization is left also inhigh resistance layers (channel forming region and offset region). Sinceelectric current can easily flow through the metallic element, aresistance of a region which should be a high resistance layer isreduced. Therefore, an off current is increased and thus variationbetween respective elements is produced, which causes deterioration inthe stability and reliability of a TFT characteristic.

In order to solve this problem, a technique (gettering technique) forremoving an metallic element for promoting crystallization from acrystalline semiconductor film is developed and disclosed in JapanesePatent Application Laid-open No. Hei 10-270363. According to thegettering technique, first, an element belonging to group 15 isselectively added to the crystalline semiconductor film and thermaltreatment is performed. By this thermal treatment, the metallic elementin a region to which the element belonging to group 15 is not added(gettered region) is emitted from the gettered region to be diffused andcaptured in a region to which the element belonging to group 15 is added(gettering region). As a result, the metallic element can be removed orreduced in the gettered region. Further, heating temperature at thegettering can be made to be 600° C. or lower which the lass substratecan withstand. Also, it is confirmed that even when not only an elementbelonging to group 15 but also an element belonging to group 13 isintroduced, the metallic element can be gettered.

The crystalline semiconductor film formed through such manufacturingsteps has high mobility. Thus, a thin film transistor (TFT) is formedusing the crystalline semiconductor film and often utilized for, forexample, an active matrix electric device.

In an active matrix liquid crystal display device, a pixel circuit forperforming image display for each functional block and a driver circuitover a single substrate for controlling the pixel circuit composed of ashift register circuit, a level shifter circuit, a buffer circuit, asampling circuit, and the like formed on the basis of a CMOS circuit asthe basics are formed.

In the pixel circuit of the active matrix liquid crystal display device,TFTs (pixel TFTs) are arranged for each of several tens to severalmillions of pixels and a pixel electrode is provided in each of thepixel TFTs. An opposing electrode is provided on an opposing substratepositioned so as to sandwich the liquid crystal therebetween to therebyform a kind of capacitor using liquid crystal as dielectric. This deviceis configured such that a voltage applied to the respective pixels iscontrolled by a switching function of a TFT to control a charge to thecapacitor to thereby drive the liquid crystal, and the amount oftransmitting light is controlled to display an image.

The pixel TFT is made from an n-channel TFT and used as a switchingelement for applying a voltage to the liquid crystal to drive it. Sincethe liquid crystal is driven by an alternating current, a method calleda frame reverse drive is employed in many cases. Since power consumptionis suppressed to be low with this method, with respect to acharacteristic required for the pixel TFT, it is important tosufficiently reduce an off current value (drain current flowing at anoff operation of the TFT).

A low concentration drain (LDD: lightly doped drain) structure is knownas a TFT structure for reducing the off current value. In thisstructure, a region to which an impurity element is added at a lowconcentration is provided between the channel forming region and thesource region or the drain region, which is formed by adding an impurityelement thereto at a high concentration. This region is called a LDDregion. Also, a so-called GOLD (gate-drain overlapped LDD) structure inwhich the LDD region is overlapped with the gate electrode through a(ate insulating film is known as means for preventing deterioration ofan on current value due to a hot carrier. It is known that with such astructure, a high electric field near the drain is relaxed to preventhot carrier injection and thus a deterioration phenomenon is effectivelyprevented.

Also, in order to obtain the GOLD structure, end portions of the gateelectrode are formed in a shape having tapers. With such a shape, a stepof introducing an impurity element for imparting an n-type to asemiconductor layer composing an n-channel TFT and a step of introducingan impurity element for providing a p-type to a semiconductor layercomposing a p-channel TFT are respectively performed by one dopingprocessing. Thus, the source region and the drain region are formed in aregion which is not overlapped with the gate electrode and LDD regionshaving concentration gradients in conformity with the shape of thetapers can be formed under the tapers of the gate electrode.

Also, energy of an ion implanted into the semiconductor film in dopingprocessing is very large as compared with bond energy of elementscomposing the semiconductor film. Thus, the element composing thesemiconductor film is flown from a lattice point by the ion implantedinto the semiconductor film to produce a defect in crystal. Therefore,after the doping processing, in order to repair the defect andsimultaneously to activate the implanted impurity element, thermaltreatment is performed in many cases. As the thermal treatment, there isa thermal annealing method using a furnace-annealing furnace, a laserannealing method, or a rapid thermal annealing method (RTA method).Also, the activation of the impurity element is an important process inorder to produce the reunions to which the impurity element is added tobe low resistance regions so that they can function as the LDD regions,the source region, and the drain region.

The element belonging to group 15 is implanted into the semiconductorfilm by an ion doping method (which is a method of dissociating PH₃ orthe like by plasma and accelerating an ion by an electric field toimplant it into the semiconductor film, in which mass separation of anion is basically not performed). When, for example, phosphorus isintroduced for gettering, a necessary phosphorus concentration is1×10²⁰/cm³ or higher. The addition of the element belonging to group 15by the ion doping method causes an amorphous state of the semiconductorfilm. However, an increase in a concentration of the element belongingto group 15 hinders recrystallization by later thermal treatment andthus this becomes a problem. Also, the addition of the element belongingto group 15 at a high concentration causes an extension of processingtime required for the doping, which is a problem since it results in areduction of a throughput in a doping step.

Further, the element belonging to group 15 is an impurity element forproviding an n-type. It is required that a concentration of an impurityelement for providing a p-type (for example, the element belonging togroup 13), which is necessary to reverse a conductivity type is 1.5times to 3 times higher than that of the element belonging to group 15,which is added to the source region and the drain region of a p-channelTFT. Thus, there is a problem in that a resistance of the source regionand the drain region is increased due to the difficulty ofrecrystallization.

SUMMARY OF THE INVENTION

The present invention is a technique for solving such problems, and anobject of the present invention is to achieve improvement of performancecharacteristics and reliability of a semiconductor device represented byan active matrix liquid crystal display device manufactured using TFTs,by effectively removing a metallic element left in a crystallinesemiconductor film obtained using the metallic element for promotingcrystallization of a semiconductor film and by performing satisfactoryrestoration of crystallinity of the semiconductor film and activation ofthe metallic element.

The present invention is characterized in that, in order to recovercrystallinity of a low concentration impurity region overlapped with aportion of the (ate electrode and to activate an impurity element, asubstrate on which a reflecting film is formed or a reflecting platemade of a material having high reflectance (hereinafter called areflector) are provided in a rear side (in this specification, it isdefined as a surface opposite to a surface on which a semiconductor filmis formed) of a substrate on which a semiconductor film is formed(hereinafter referred to as a semiconductor film substrate) and laserlight is irradiated from a front side (in this specification, it isdefined as a surface on which a semiconductor film is formed) of thesemiconductor film substrate and the laser light transmitted through thesemiconductor film substrate is reflected by the reflector and then thelaser light is irradiated again, this time from the rear side of thesemiconductor film substrate. At this time, the substrate may be heatedto about 450° C. When the substrate is heated simultaneous with theirradiation of laser light, the recovery of crystallinity of thesemiconductor film and the activation of the impurity element can bemore effectively performed.

The low concentration impurity region described above is a region intowhich an impurity of one conductivity type is introduced. The elementbelonging to group 15 or the element belonging to group 13 is used asthe one conductivity type impurity. In addition, hydrogen may be addedto the low concentration impurity region and both one conductivity typeimpurity and hydrogen are included in the low concentration impurity reregion.

Also, the element belonging to group 15 and the element belonging togroup 13 may be added to the low concentration impurity region, and thusboth the element belonging to group 15 and the element belonging togroup 13 are included in the impurity region.

Also, the element belonging to group 15, the element belonging to group13, and hydrogen may be added to the low concentration impurity region,and thus both the element belonging to group 15, the element belongingto group 13, and hydrogen are included in the impurity region.

Further the present invention is characterized in that a semiconductorfilm is crystallized using a metallic element for promotingcrystallization, an impurity region to which a noble gas element (alsocalled a noble gas) is added is formed, and the metallic elementincluded in the semiconductor film is segregated to the impurity regionby thermal treatment to thereby perform gettering, and subsequently areflector is provided in a rear side of a semiconductor film substrate,and laser light is irradiated from a front side of the semiconductorfilm substrate to irradiate laser light from the rear side of thesemiconductor film substrate.

When the noble gas is used, the introduction amount of impurity elementscan be reduced. Thus, damages to the gate insulating film, thesemiconductor film, and an interface therebetween due to dopingprocessing can be reduced and trap centers can be decreased. Therefore,reliability in manufacture of a TFT can be improved. Also, since thetrap centers are decreased, a width of an overlap region between thegate electrode and the low concentration impurity region can beshortened. Thus, a transistor can be further microfabricated.

As the noble gas element, there may be used one kind or plural kinds ofelements selected from the group consisting of He, Ne, Ar, Kr, and Xe.When these ions are accelerated by an electric field to introduce itinto the semiconductor film, a dangling bond and a lattice distortionare produced and thus a gettering cite can be produced.

Also, one conductivity type impurity may be added to the impurity regionto which the noble gas element is added, and thus both the noble gaselement and one conductivity type impurity are included in the impurityregion. The element belonging to group 15 or the element belonging togroup 13 is applied as the one conductivity type impurity. In addition,hydrogen may be added to the impurity region, and thus the noble gaselement, one conductivity type impurity, and hydrogen are included inthe impurity region.

Also, the element belonging to group 15 and the element belonging togroup 13 may be added to the impurity region to which the noble gaselement is added, and thus the noble gas element, the element belongingto group 15, and the element belonging to group 13 are included in theimpurity region.

Also, the element belonging to group 15, the element belonging to group13, and hydrogen may be added to the impurity region to which the noblegas element is added, and thus the noble gas element, the elementbelonging to group 15, the element belonging to group 13, and hydrogenare included in the impurity region.

Also, the reflector may be provided in contact with the semiconductorfilm substrate or may be provided to be physically separated from thesemiconductor film substrate.

The present invention is also characterized in that a material which isresistant to heat and has a high reflectance with respect to the laserbeam is used as a material for forming the reflector. As shown in FIG.5, the reflector may be made of an element selected from the groupconsisting of aluminum (Al), tungsten (W), tantalum (Ta), titanium (Ti),chromium (Cr), and silver (Al), a compound including the element, or analloy including the element. A reflecting film may be formed on thesubstrate as the reflector. Also, a reflecting plate made of a materialhaving high reflectance may be used as the reflector.

As regards the reflector, a surface thereof by which the laser light isreflected may be a plane surface or a curved surface. The laser light iscondensed on or near the surface of the semiconductor film formed on thesubstrate. Also, a part of the laser light is transmitted through thesubstrate and reflected by the reflector to be irradiated onto thesemiconductor film also from a rear side thereof. At this time, when thesurface of the reflector, by which the laser light is reflected, forms aplane surface, there may be a case where the laser light reflected bythe reflector becomes more spread or scattered as compared with laserlight incident from the front side of the semiconductor film. Thus, whenthe surface of the reflector by which the laser light is reflected isformed as a curved surface, laser light which is reflected from thereflector and condensed can be irradiated from the rear side of thesemiconductor film and thus an effective energy density in thesemiconductor film can be further increased. Since the curvature of thecurved surface is dependent on a state of laser light, a distancebetween the substrate and the reflector, and the like, it may beappropriately determined by an operator. Also, rugged portions may beprovided on a reflecting surface of the reflector to effect diffusereflection of the laser light.

Also, when irradiating laser light to the substrate from the front sideof the substrate on which the semiconductor film is formed, thesubstrate and the reflector may be moved relative to the laser light.Alternatively, only the substrate may be moved relative to the laserlight and the reflector.

Also, it is an essential condition that the laser light used in thepresent invention be able to transmit through the substrate. FIG. 6Ashows transmittance of a 1737 glass substrate with respect to awavelength and FIG. 6B shows transmittance of a synthetic quartz glasssubstrate with respect to a wavelength. From FIGS. 6A and 6B, if sometransmittance is required for the substrate to be used, a wavelength ofthe laser beam is desirably 300 nm or more (preferably, 400 nm or more).Also, from FIGS. 6A and 6B, the substrate is desirably selected inaccordance with the laser to be used. For example, when an XeCl excimerlaser (308 nm in wavelength) is used, since the transmittance of thesynthetic quartz glass substrate is higher than that of the 1737 glasssubstrate, it is preferable to use the synthetic quartz glass substrate.Further, a solid laser rather than a gas laser is desirably used as thelaser. This reason is as follows. That is, gas used for the gas laser isgenerally quite expensive, and thus when a frequency of gas exchange ishigh, there is a problem in that it increases manufacturing cost. Also,exchange of attached devices such as a laser tube for laser oscillationand a gas purifying unit for removing an unnecessary compound producedin an oscillation process are required once even two to three years.These attached devices are often expensive, which also causes anincrease in manufacturing cost such as described above. Thus, when thesolid laser (laser for outputting a laser beam using a crystal rod as aresonant cavity) such as a YAG laser is used, a running cost (here,which means a cost produced with operation) can be reduced as comparedwith the gas laser.

Also, when irradiating the laser light to the semiconductor filmsubstrate from the front side of the semiconductor film substrate, thelaser light may be irradiated to the semiconductor film substrate at aslant angle.

Also, when the reflector is manufactured once, it can be reused manytimes.

Also, there is an amorphous semiconductor film or a crystallinesemiconductor film as the semiconductor film. A compound semiconductorfilm having an amorphous structure, such as an amorphous silicongermanium film may also be used other than the amorphous semiconductorfilm.

Thus, when the present invention is applied, the semiconductor film forwhich gettering of the metallic element, the recovery of crystallinityof the semiconductor film, and the activation of the impurity elementhas been satisfactorily performed can be obtained and the performance ofa semiconductor device can be greatly improved. For example, in the caseof a TFT, when the metallic element is sufficiently gettered, an offcurrent value is reduced and variation in the off current value can besuppressed. Also, when the crystallinity of the semiconductor film issufficiently recovered, the channel forming region becomes a highresistance region and a leak current can be reduced. Also, when theimpurity element is sufficiently activated, the regions to which theimpurity element is added are formed as low resistance regions whichfunction as the LDD region, the source region, and the drain region.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A and 1B show a structure of a laser apparatus of the presentinvention;

FIGS. 2A and 2B show a structure of an optical system of the laserapparatus of the present invention;

FIG. 3 shows an example of a laser annealing method of the presentinvention;

FIGS. 4A to 4C show manufacturing steps of a TFT having a GOLD structureof the present invention;

FIG. 5 is a graph indicating reflectance to a wavelength in examples ofreflecting materials of the present invention;

FIG. 6A is a graph indicating transmittance to a wavelength in a 1737glass substrate and FIG. 6B is a graph indicating transmittance to awavelength in a synthetic quartz glass substrate;

FIGS. 7A to 7D show manufacturing steps of the TFT having the GOLDstructure of Embodiment 2;

FIGS. 8A to 8C are cross sectional views indicating an example ofmanufacturing steps of pixel TFTs and TFTs of a driver circuit ofEmbodiment 5;

FIGS. 9A to 9C are cross sectional views indicating an example ofmanufacturing steps of the pixel TFTs and the TFTs of the driver circuitof Embodiment 5;

FIGS. 10A to 10C are cross sectional views indicating an example ofmanufacturing steps of the pixel TFTs and the TFTs of the driver circuitof Embodiment 5;

FIG. 11 is a cross sectional view indicating an example of manufacturingsteps of the pixel TFTs and the TFTs of the driver circuit of Embodiment5;

FIG. 12 is a top view of a pixel in a pixel portion of Embodiment 5;

FIG. 13 is a cross sectional view indicating manufacturing steps of anactive matrix liquid crystal display device of Embodiment 6;

FIG. 14 is a cross sectional structural view of a driver circuit and apixel portion in a light emitting device of Embodiment 8;

FIG. 15A is a top view of a light emitting device and FIG. 15B is across sectional structural view of a driver circuit and a pixel portionin the light emitting, device of Embodiment 8;

FIGS. 16A to 16F show examples of semiconductor devices of Embodiment10;

FIGS. 17A to 17D show examples of semiconductor devices of Embodiment10;

FIGS. 18A to 18C show examples of semiconductor devices of Embodiment10;

FIG. 19 shows an example of a laser annealing method of the presentinvention;

FIGS. 20A to 20D show manufacturing steps of the TFT having the GOLDstructure of Embodiment 3;

FIG. 21 is a cross sectional view indicating manufacturing steps of anactive matrix liquid crystal display device of Embodiment 7;

FIG. 22 is a cross sectional structural view of a pixel portion of alight emitting device of Embodiment 9; and

FIGS. 23A to 23D show manufacturing steps of a TFT and an example oflaser annealing of Embodiment 4.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[Embodiment Mode]

An embodiment mode of the present invention will be described. FIG. 1Ashows a structure of a laser irradiation apparatus. This laserirradiation apparatus has a laser oscillator 101 (Nd:YAG laser in thisembodiment mode), an optical system 201 for linearly processing laserlight 210 (second harmonic, third harmonic or fourth harmonic,preferably, the second harmonic) from the laser oscillator 101 as anoscillation source, and a stage 102 for holding a translucent substrate.A heater 103 and a heater controller 104 is provided in the stage 102and thus the substrate can be heated to 450° C. Also, a reflector 105 isprovided on the stage 102 and a substrate 106 on which a semiconductorfilm is formed is located thereon.

Note that, when the laser light outputted from the laser oscillator 101is to be modulated to the second harmonic or the third harmonic, awavelength modulator including a non-linear element may be providedimmediately after the laser oscillator 101.

Next, a method of holding the substrate 106 in the laser irradiationapparatus having the structure as shown in FIG. 1A will be describedusing FIG. 1B. The substrate 106 held in the stage 102 is located in areaction chamber 107 and then linear laser light from the laseroscillator 101 as an oscillation source is irradiated thereto. The innerportion of the reaction chamber can be made to be in a reduced pressurestate or in an inert gas atmosphere by an evacuation system or a gassystem (both are not shown). The semiconductor film can be heated at100° C. to 450° C. without contaminating it.

Also, the stage 102 can be moved along guide rails 108 in the reactionchamber 107 and thus the linear laser light can be irradiated onto theentire surface of the substrate. The laser light is made incident from awindow (not shown) made of quartz, which is provided in the top side ofthe substrate 106. In FIG. 1B, a transfer chamber 109 is connected withthe reaction chamber 107, an intermediate chamber 110 is connected withthe transfer chamber 109, and a load and unload chamber 111 is connectedwith the intermediate chamber 110. The reaction chamber 107 and thetransfer chamber 109 are isolated from each other by a gate valve 113.The intermediate chamber 110 and the load and unload chamber 111 areisolated from each other by a gate valve 112.

A cassette 114 capable of holding a plurality of substrates is locatedin the load and unload chamber 111 and the substrate is transferred by atransfer robot 115 provided in the transfer chamber 109. A substrate106′ indicates a substrate which is being transferred. With such astructure, laser annealing, processing can be successively performed ina reduced pressure state or in an inert gas atmosphere.

Next, a structure of the optical system 201 for processing laser lightinto linear light will be described using FIGS. 2A and 2B. FIG. 2A showsthe optical system 201 viewed from the side and FIG. 2B shows theoptical system 201 viewed from the top.

Laser light from the laser oscillator 101 as an oscillation source isdivided in a vertical direction by a cylindrical array lens 202. Thedivided laser light is further divided in a transverse direction by acylindrical array lens 203. That is, in the end the laser light isdivided in a matrix by the cylindrical array lenses 202 and 203.

Then, the laser light is temporarily condensed by a cylindrical lens204. Then, the laser light passes through a cylindrical lens 205immediately after the cylindrical lens 204. After that, the laser lightis reflected by a mirror 206 and passed through a cylindrical lens 207to reach an irradiation surface 208.

At this time, the laser light projected onto the irradiation surface 208indicates a linear irradiation surface. That is, this means that a crosssectional shape of the laser light transmitted through the cylindricallens 207 becomes linear. Homogenization the linearly processed laserlight in a width direction (short length direction) is made by thecylindrical array lens 202 and the cylindrical lenses 204 and 207. Also,homogenization of the above laser light in a length direction (long,length direction) is made by the cylindrical array lens 203 and the,cylindrical lens 205.

Next, a structure for irradiating laser light onto the semiconductorfilm, which is formed on the substrate, from the rear side thereof willbe described using FIG. 3. FIG. 3 shows a positional relationshipbetween the substrate 106 and the reflector 105 in FIG. 1A.

In FIG. 3, reference numeral 311 denotes a substrate with a TFT having aGOLD structure after the gate electrode is formed. Also, a reflector 312for reflecting laser light is located under the substrate 311.

Here, a method of performing steps up to formation of the gate electrodeof the TFT will be described using FIGS. 4A to 4C. First, a glasssubstrate, a synthetic quartz glass substrate, a crystallized glasssubstrate, or a plastic substrate is used as a translucent substrate300. An insulating film including silicon such as a silicon oxide filmor a silicon oxynitride film (SiOxNy), which is formed by a knownprocess (sputtering method, LPCVD method, plasma CVD method, or thelike) may be used as a base insulating film 301. Of course, other typesof insulating films may be used. Also, the base insulating film may havenot only a single layer structure but also a laminate structure.

Then, a semiconductor film 302 having an amorphous structure is formedat a thickness of 25 to 80 nm (preferably, 30 to 60 nm) by a known means(sputtering, method, LPCVD method, plasma CVD method, or the like). Amaterial of the semiconductor film is not limited to a specificmaterial. However, the semiconductor film is preferably made of silicon,a silicon germanium (SiGe) alloy, or the like. After that, a metallicelement for promoting crystallization (one kind or plural kinds ofelements selected from the group consisting of Fe, Co, Ni, Ru, Rh, Pd,Os, Ir, Pt, Cu, Ag, Au, Sn, and Sb) is added to the semiconductor filmto form a metal-containing layer 303 and thermal treatment is performedto crystallize the semiconductor film. Of course, another knowncrystallization method (such as a laser crystallization method) may becombined. (FIG. 4A)

After the crystallized semiconductor film is patterned to form anisland-like semiconductor film 304, an insulating film including siliconsuch as a silicon oxide film or a silicon oxynitride film (SiOxNy) isformed as an insulating film 305 and then a conductive film 306 isformed. A material of the conductive film is not limited to a specificmaterial. However, the conductive film may be made of an elementselected from the group consisting of Ta, W, Ti, Mo, Al, Cu, Cr, and Nd,an alloy material or a compound material containing the element as itsmain component. A semiconductor film represented by a crystallinesilicon film doped with an impurity element such as phosphorus may beused as the conductive film. Also, an AgPdCu alloy may be used. Ofcourse, the conductive film may be made have not only a single layerstructure but also a laminate structure. Subsequently, etching isperformed to form a gate electrode 307 in which tapers are formed in endportions. (FIG. 4B)

Then, doping is performed for impurity element introduction. Accordingto the doping processing, one kind or plural kinds of elements selectedfrom noble gas elements, and an impurity element for providing an n-typeor an impurity element for providing a p-type are introduced into thesemiconductor film by an ion doping method, an ion implantation method,or the like. Alternatively, one kind or plural kinds of elementsselected from noble gas elements, and an impurity element for providingan n-type and an impurity element for providing a p-type may beintroduced. In addition, hydrogen may also be added. Of course, a stepof introducing a noble gas element maybe performed separately from astep of introducing an impurity element for providing an n-type or animpurity element for providing a p-type. By the doping processing,regions 308 into which the impurity element is introduced at a highconcentration, regions 309 into which the impurity element is introducedat a tow concentration due to the tapers provided in the end portions ofthe gate electrode, and a region (channel forming, region 310 into whirlthe impurity element is not introduced are formed. Then, thermaltreatment is performed for gettering the metallic element. By thethermal treatment, the metallic element is moved from the channelforming, region to the reunions to which the impurity element is addedand thus the channel forming region can be made to be a high resistanceregion.

A method for sufficiently restoring the crystallinity of the region intowhich the noble gas element is introduced is shown in FIG. 3.

Here, the reflector 312 may be a substrate such that a metallic film isformed on the surface thereof (reflecting surface of laser light) or maybe a reflecting plate made of a material having high reflectance. Inthis case, any material may be used for the metallic film. Typically, ametallic film including any element selected from the group consistingof aluminum, silver, tungsten, titanium, and tantalum is used.

Also, instead of disposing the reflector 312, the metallic film such asdescribed above may be directly formed on the rear surface (surfaceopposite to the front surface) of the substrate 300 to thereby reflectlaser light. Note that this structure is allowed on the condition thatthe metallic film formed on the rear surface is not removed in amanufacturing process of a semiconductor device.

Then, the laser light linearly processed through the optical system 201(of which only the cylindrical lens 207 is shown in the drawings)described using FIGS. 2A and 2B is irradiated also to the semiconductorfilm located under the gate electrode 307.

At this time, the laser light irradiated to the semiconductor filmincludes laser light 313 directly irradiated thereto after passingthrough the cylindrical lens 207 and laser light 314 irradiated theretoafter it is reflected by the reflector 312. Note that in thisspecification, laser light irradiated onto the surface of the reflectoris called first laser light and laser light reflected by the reflectoris called second laser light.

With respect to the laser light transmitted through the cylindrical lens207, it forms an incidence angle of 45° to 90° relative to the surfaceof the substrate in a condensing process thereof. Thus, the second laserlight 314 can be diffracted to reach the rear surface side of thesemiconductor film and irradiated thereon. Also, when rugged portionsare formed on the reflecting surface of the reflector 312 to effectdiffuse reflection of the laser light, the second laser light 314 can beobtained more efficiently %. When the reflecting surface of thereflector 312 is made to be a curved surface (for example, a concavesurface), the laser light can be irradiated onto the semiconductor filmwhile being condensed, and thus it is efficient.

As described above, according to the present invention, the laser lightfrom the solid laser as the oscillation source can be linearly processedand the processed linear laser light can be divided into the first laserlight and the second laser light to irradiate the laser light onto therear surface of the semiconductor film. Further, although the sourceregion and the drain region are required to be regions having lowerresistance as compared with the LDD regions, since the first laser lightand the second laser light are irradiated, the impurity element issufficiently activated.

Further, since the heater 103 and the heater controller 104 are providedin the stage 102 of the laser irradiation apparatus, it is possible toirradiate the laser light while heating the substrate at 100° C. to 450°C. Thus, the recovery of crystallinity and the activation of theimpurity element can be performed more efficiently.

Also, as shown in FIG. 19, when the laser light is irradiated to thesemiconductor film substrate at a slant angle, the second laser lightcan be easily irradiated onto the semiconductor film overlapped with thegate electrode, and thus the recovery of crystallinity of thesemiconductor film and the activation of the impurity element issufficiently performed.

The present invention having the above structure will be described inmore detail based on embodiments described hereinbelow.

[Embodiment 1]

An embodiment of the present invention will be described. FIG. 1A showsa structure of a laser irradiation apparatus. This laser irradiationapparatus has a laser oscillator 101, an optical system 201 for linearlyprocessing laser light 210 (preferably, the second harmonic) from thelaser oscillator 101 as an oscillation source, and a stage 102 forholding a translucent substrate. A heater 103 and a heater controller104 is provided in the stage 102 and thus the substrate can be heated at100° C. to 450° C. Also, a reflector 105 is provided on the stage 102and a substrate 106 on which a semiconductor film is formed is locatedthereon.

Note that, when the laser light outputted from the laser oscillator 101is to be modulated to the second harmonic or the third harmonic, awavelength modulator including a non-linear element may be providedimmediately after the laser oscillator 101. In this embodiment, anNd:YAG laser is used as the laser oscillator 101 and laser lightmodulated to the second harmonic by the non-linear optical element isused. However, the Nd:YAG laser is a laser having high coherentproperty. Thus, it is desirable that a thin film polarizer (TFP), apolarizing plate, and the like are provided before the optical system201 so that an optical path length of a part of the laser light emittedfrom the laser oscillator 101 may be extended to thereby prevent aninterference in an irradiation surface.

Next, a method of holding the substrate 106 in the laser irradiationapparatus having the structure as shown in FIG. 1A will be describedusing FIG. 1B. The substrate 106 held in the stage 102 is located in areaction chamber 107 and then linear laser light from the laseroscillator 101 as an oscillation source is irradiated thereto. The innerportion of the reaction chamber can be made to be in a reduced pressurestate or in an inert gas atmosphere by an evacuation system or a gassystem (both are not shown). Thus, the semiconductor film can be heatedat 100° C. to 450° C. without contaminating it.

Also, the stage 102 can be moved along guide rails 108 within thereaction chamber and thus the linear laser light can be irradiated ontothe entire surface of the substrate. The laser light is made incidentfrom a window (not shown) made of quartz, which is provided in the topside of the substrate 106. In FIG. 1B, a transfer chamber 109 isconnected with the reaction chamber 107, an intermediate chamber 110 isconnected with the transfer chamber 109, and a load and unload chamber111 is connected with the intermediate chamber 110. The reaction chamber107 and the transfer chamber 109 are isolated from each other by a gatevalve 113. The intermediate chamber 110 and the load and unload chamber111 are isolated from each other by a gate valve 112.

A cassette 114 capable of holding a plurality of substrates is locatedin the load and unload chamber 111 and the substrate is transferred by atransfer robot 115 provided in the transfer chamber 109. A substrate106′ indicates a substrate which is being transferred. With such astructure, laser annealing processing can be successively performed in areduced pressure state or in an inert gas atmosphere.

Next, a structure of the optical system 201 for processing laser lightinto linear light will be described using FIGS. 2A and 2B. FIG. 7A showsthe optical system 201 viewed from the side and FIG. 2B shows theoptical system 201 viewed from the top.

Laser light from the laser oscillator 101 as an oscillation source isdivided in a vertical direction by a cylindrical array lens 202. Thedivided laser light is further divided in a transverse direction by acylindrical array lens 203. That is, in the end the laser light isdivided in a matrix by the cylindrical array lenses 202 and 203.

Then, the laser light is condensed by a cylindrical lens 204. Then, thelaser light passes through a cylindrical lens 205 immediately after thecylindrical lens 204. After that, the laser light is reflected by amirror 206 and passed through a cylindrical lens 207 to reach anirradiation surface 208.

At this time, the laser light projected onto the irradiation surface 208indicates a linear irradiation surface. That is, this means that a crosssectional shape of the laser light transmitted through the cylindricallens 207 becomes linear. Homogenization of the linearly processed laserlight in a width direction (short length direction) is made by thecylindrical array lens 202 and the cylindrical lenses 204 and 207. Also,homogenization of the above laser light in a length direction (longlength direction) is made by the cylindrical array lens 203 and thecylindrical lens 205.

Next, a structure for irradiating laser light from the rear side of thesubstrate to the semiconductor film formed on the substrate will bedescribed using FIG. 3. FIG. 3 shows a positional relationship betweenthe substrate 106 and the reflector 105 in FIG. 1A.

In FIG. 3, reference numeral 311 denotes a substrate having a TFT afterthe gate electrode is formed thereon. Also, a reflector 312 forreflecting laser light is located under the substrate 311.

Here, a method of performing steps until the gate electrode of the TFTis formed will be described using FIGS. 4A to 4C. First, a glasssubstrate, a synthetic quartz glass substrate, a crystallized glasssubstrate, or a plastic substrate is used as a translucent substrate300. In this embodiment, a synthetic quartz glass substrate is used asthe translucent substrate 300.

Then, an insulating film containing silicon such as a silicon oxide filmor a silicon oxynitride film (SiOxNy), which is formed by a known means(sputtering method, LPCVD method, plasma CVD method, or the like) ispreferably used as a base insulating film 301. Of course, the baseinsulating film may have not only a single layer structure but also alaminate structure. In this embodiment, a silicon oxide film is formedat a film thickness of 150 nm by a plasma CVD method.

Then, a semiconductor film 302 having an amorphous structure is formedat a thickness of 25 to 80 nm (preferably, 30 to 60 nm) by a known means(sputtering method, LPCVD method, plasma CVD method, or the like). Amaterial of the semiconductor film is not limited to a specificmaterial. However, the semiconductor film is preferably made of silicon,a silicon germanium (SiGe) alloy, or the like. In this embodiment, anamorphous silicon film is formed at a film thickness of 50 nm by aplasma CVD method. After that, a metallic element for promotingcrystallization is added to the semiconductor film to form a metalcontaining layer 303. Plasma processing, evaporation, a sputteringmethod, ion implantation, solution coating, or the like is preferablyused as a method of introducing the metallic element into thesemiconductor film. In this embodiment, a nickel acetate aqueoussolution (5 ppm in weight conversion concentration and 5 ml in volume)is applied onto the surface of the amorphous silicon film by a spin coatmethod. Then, thermal treatment is performed to crystallize thesemiconductor film. Since the heating time and the heating temperaturevary depending on the semiconductor film and the metallic element to beadded, those are preferably determined as appropriate by an operator. Inthis embodiment, it is exposed at 550° C. in an nitrogen atmosphere for4 hours. After the crystallized semiconductor film is patterned to forman island-like semiconductor film 304, an insulating film includingsilicon such as a silicon oxide film or a silicon oxynitride film(SiOxNy) is formed as an insulating film 305 by a known means(sputtering method, LPCVD method, plasma CVD method, or the like).

Subsequently, a conductive film 306 is formed. A material of theconductive film 306 is not limited to a specific material. However, theconductive film 306 may be made of an element selected from the groupconsisting of Ta, W, Ti, Mo, Al, Cu, Cr, and Nd, an alloy materialincluding mainly the above element, or a compound material includingmainly the above element. A semiconductor film represented by acrystalline silicon film doped with an impurity element such asphosphorus may be used as the conductive film. An AgPdCu alloy may bealso used. Of course, the conductive film may have not only a singlelayer structure but also a laminate structure. In this embodiment, theconductive film 306 made from a W film having a film thickness of 400 nmis formed. The W film is formed by a sputtering method using W as atarget. In addition, the W film can be formed by a thermal CVD methodusing tungsten hexafluoride (WF₆).

Subsequently, etching is performed to form a gate electrode 307 in whichtapers are formed in end portions. A mask (not shown) made of a resistis formed by a photolithography method and etching processing isperformed for forming an electrode and a wiring. In this embodiment, anICP (inductively coupled plasma) etching method is used for etchingprocessing and CF₄, Cl₂, and O₂ are used as etching gases and a ratio ofrespective gas flow rates is set to be 25:25:10 (sccm). RF power having500 W and 13.56 MHz is supplied to a coil type electrode at a pressureof 1 Pa to produce plasma and to thus perform etching. Here, a dryetching apparatus (Model E645-□ICP) using ICP, which is produced byMatsushita Electronic industrial Co., Ltd. is used. Also, RF powerhaving 150 W and 13.56 MHz is supplied to a substrate side (samplestage) to apply a substantially negative self bias voltage. The W filmis etched by this etching processing to form end portions of theconductive layer in taper shapes. Note that, in order to perform etchingwithout leaving the residue on the gate insulating film, an etching timeis preferably increased by about 10% to 20%. In the above etchingprocessing, when a shape of the mask made of a resist is suitable, theend portions of the conductive layer becomes taper shapes by an effectof the bias voltage applied to the substrate side. An angle of the taperportions becomes 15° to 45°. Reference numeral 304 denotes a gateinsulating film. A region which is not covered with the conductive layer306 is etched at about 20 nm to 50 nm to become a thinner region.

Then, doping is performed for impurity element introduction. Accordingto the doping processing, one kind or plural kinds of elements selectedfrom noble gas elements and an impurity element for providing an n-typeor an impurity element for providing a p-type are introduced into thesemiconductor film by an ion doping method, an ion implantation method,or the like. Also, one kind or plural kinds of elements selected fromnoble gas elements, an impurity element for providing an n-type, and animpurity element for providing a p-type may be introduced. In addition,hydrogen may be added. Of course, a step of introducing a noble gaselement may be performed separately from a step of introducing animpurity element for providing an n-type or an impurity element forproviding a p-type. By the doping processing, regions 308 into which theimpurity element is introduced at a high concentration, regions 309 intowhich the impurity element is introduced at a low concentration due tothe tapers in the end portions of the (ate electrode, and a region(channel forming region) 310 into which the impurity element is notintroduced are formed. In this embodiment, phosphorus is used as anelement belonging to group 15 in the periodic table and argon is used asa noble gas element. With respect to all implantation condition ofphosphorus, 5% PH₃ diluted with hydrogen is used, an accelerating,voltage is set to be 80 keV, and a dose is set to be 1.5×10¹⁵/cm². Atime required for implantation is about 8 minutes and thus phosphoruscan be implanted into the crystalline semiconductor film at an averageconcentration of 2×10²⁰/cm³. On the other hand, argon is implanted at anaccelerating voltage of 90 keV and a dose of 2×10¹⁵/cm².

Subsequently, thermal treatment is performed for gettering the metallicelement. The metallic element is moved from the channel forming regionto the regions to which the impurity element is added by the thermaltreatment and thus the channel forming region can be produced as a highresistance region. In this embodiment, thermal treatment is performedfor gettering in a nitrogen atmosphere at 550° C. for 4 hours.

A method of sufficiently recovering the crystallinity of the region intowhich the noble gas element is introduced is shown in FIG. 3.

Here, the reflector 312 may be a substrate such that a metallic film isformed on the surface thereof (reflecting surface of laser light) or maybe a reflecting plate made of a material having high reflectance. Inthis case, any metallic material may be used for the metallic film.Typically, a metallic film containing any element selected from thegroup consisting of aluminum, silver, tungsten, titanium, and tantalumis used.

Also, instead of disposing the reflector 312, the above metallic filmcan be directly formed on the rear surface (surface opposite to thefront surface) of the substrate 300 to reflect laser light therefrom.Note that this structure is allowed on the condition that the metallicfilm formed on the rear surface is not removed in a manufacturingprocess of a semiconductor device. In this embodiment, A syntheticquartz glass substrate on which aluminum is formed by sputtering is usedas the reflector.

Then, the laser light linearly processed through the optical system 201(of which only the cylindrical lens 207 is shown in the drawings)described using FIGS. 2A and 2B is also irradiated to the semiconductorfilm located under the gate electrode 307.

At this time, the laser light irradiated to the semiconductor filmincludes laser light 313 directly irradiated thereto through thecylindrical lens 207 and laser light 314 irradiated thereto after it isreflected from the reflector 312. Note that in this specification, laserlight irradiated onto the surface of the reflector is called first laserlight and laser light reflected from the reflector is called secondlaser light.

With respect to the laser light transmitted through the cylindrical lens207, it forms an incidence angle of 45° to 90° relative to the surfaceof the substrate in a condensing process. Thus, the second laser light314 is also diffracted to the rear side of the semiconductor film andirradiated thereon. Also, when rugged portions are provided on thereflecting surface of the reflector 312 to effect diffuse reflection ofthe laser light, the second laser light 314 can be obtained with higherefficiency. When the reflecting surface of the reflector 312 is made tobe a concave surface, the laser light can be irradiated to thesemiconductor film while condensing it, and thus it is efficient.

As described above, according to this embodiment, the laser light fromthe solid laser as the oscillation source can be linearly processed andthe processed laser light can be divided into the first laser light andthe second laser light to irradiate the laser light to the rear surfaceof the semiconductor film. Further, although the source region and thedrain region are required to be lower resistance regions as comparedwith the LDD regions, since the first laser light and the second laserlight are irradiated to the semiconductor film, the recovery ofcrystallinity and the activation of the impurity element can besufficiently performed.

Further, since the heater 103 and the heater controller 104 are includedin the stage 102 of the laser irradiation apparatus, it is possible toirradiate the laser light while the substrate is heated to about 450° C.and the recovery of crystallinity and the activation of the impurityelement can be made with higher efficiency.

[Embodiment 2]

In this embodiment, the case where laser annealing is performed for asemiconductor film substrate obtained through manufacturing stepsdifferent from Embodiment 1 will be described.

Here, a method of performing steps until the gate electrode of the TFTis formed will be described using FIGS. 7A to 7D. First, the state shownin FIG. 4A is obtained in accordance with Embodiment 1. Note that astate shown in FIG. 7A is the same state as in FIG. 4A.

Then, first thermal treatment is performed to crystallize asemiconductor film. Since the heating time and the heating temperatureare dependent on the semiconductor film and the metallic element to beadded, those are preferably determined as appropriate by an operator. Inthis embodiment, the semiconductor film is exposed at 550° C. in annitrogen atmosphere for 4 hours.

Successively, a mask 755 is formed and first doping processing isperformed to selectively introduce an impurity element into thesemiconductor film. According to the doping processing, one kind orplural kinds of elements selected from noble gas elements and animpurity element for providing an n-type or an impurity element forproviding a p-type are introduced into the semiconductor film by an iondoping method, an ion implantation method, or the like. One kind orplural kinds of elements selected from noble gas elements, an impurityelement for providing an n-type, and an impurity element for providing ap-type may be introduced in addition, hydrogen may be added. In thisembodiment, first, only argon is implanted at an accelerating voltage of90 keV and a dose of 2×10¹⁵/cm² by an ion doping method.

Then, second thermal treatment is performed to move the metallic elementused for promoting crystallization to a region 756 into which theimpurity element is introduced (gettering). In this embodiment, thermaltreatment is performed for gettering in a nitrogen atmosphere at 550° C.for 4 hours. (FIG. 7B)

The region 756 in which the metallic element is gettered is etched andthe mask is removed to form a semiconductor layer 757. Then, aninsulating film including silicon such as a silicon oxide film or asilicon oxynitride film (SiOxNy) is formed as an insulating film 758 bya known process (sputtering method, LPCVD method, plasma CVD method, orthe like).

Subsequently, a conductive film 759 is formed. A material of theconductive film is not limited to a specific material. However, theconductive film may be made of an element selected from the groupconsisting of Ta, W, Ti, Mo, Al, Cu, Cr, and Nd, an alloy materialincluding mainly the above element, or a compound material includingmainly the above element. A semiconductor film represented by acrystalline silicon film doped with an impurity element such asphosphorus may be used as the conductive film. An AgPdCu alloy may bealso used. Of course, the conductive film may be made from not only asingle layer but also a laminate. In this embodiment, the conductivefilm 759 made from a W film having a film thickness of 400 nm is formed.The W film is formed by a sputtering method using W as a target. (FIG.7C)

Subsequently, etching is performed to form a gate electrode 760 in whichtapers are formed in end portions. A mask (not shown) made of a resistis formed by a photolithography method and etching processing isperformed for forming an electrode and a wiring. In the above etchingprocessing, when a shape of the mask made of a resist is suitable, theend portions of the conductive layer becomes taper shapes by an effectof the bias voltage applied to the substrate side. An angle of the taperportions becomes 15° to 45° Reference numeral 758 denotes a (ateinsulating film. A region which is not covered with the conductive layer(gate electrode) 760 is etched at about 20 nm to 50 nm to form a thinnerregion.

Then, doping processing is performed for impurity element introduction.According to the doping processing, an impurity element for providing ann-type or an impurity element for providing a p-type is introduced intothe semiconductor film by an ion doping method, an ion implantationmethod, or the like. By the doping processing, regions 761 into whichthe impurity element is introduced at a high concentration, regions 762into which the impurity element is introduced at a low concentration bythe tapers in the end portions of the gate electrode, and a region(channel forming region) 763 into which the impurity element is notintroduced are formed. In this embodiment, phosphorus is used as anelement belonging to the group 15. With respect to an implantationcondition of phosphorus, 5% PH₃ diluted with hydrogen is used, anaccelerating voltage is set to be 80 keV, and a dose is set to be1.5×10¹⁵/cm². A time required for implantation is about 8 minutes, andthus phosphorus can be implanted into the crystalline semiconductor filmat an average concentration of 2×10²¹/cm³.

Then, thermal treatment is performed for gettering the above-mentionedmetallic element. The metallic element is moved from the channel formingregion to the region to which the impurity element is added by thethermal treatment, and thus the channel forming region can be producedas a high resistance region. In this embodiment, thermal treatment isperformed for gettering in a nitrogen atmosphere at 550° C. for 4 hours.(FIG. 7D)

Then, the recovery of crystallinity of the region into which theimpurity element is introduced and the activation of the impurityelement are made by the method shown in FIG. 3, which is described inEmbodiment 1.

Here, the reflector 312 may be a substrate such that a metallic film isformed on the surface thereof (reflecting surface of laser light) or maybe a reflecting plate made of a material having high reflectance. Inthis case, any material may be used for the metallic film. Typically, ametallic film including any element selected from the group consistingof aluminum, silver, tungsten, titanium, and tantalum is used.

Further, since the heater 103 and the heater controller 104 are includedin the stage 102 of the laser irradiation apparatus, it is possible toirradiate the laser light while heating the substrate to about 450° C.and thus the recovery of crystallinity and the activation of theimpurity element can be performed with higher efficiency.

[Embodiment 3]

In this embodiment, the case where laser annealing is performed for asemiconductor film substrate obtained through manufacturing stepsdifferent from Embodiment 1 and Embodiment 2 will be described.

Here, a method of performing steps up to formation of the gate electrodeof the TFT will be described using FIGS. 20A-20D. First, the state shownin FIG. 4A, in which a semiconductor film 302 is formed, is obtained inaccordance with Embodiment 1. Note that the same reference numerals areused in FIG. 20A for the parts corresponding to those in FIG. 4A.

An insulating film including silicon such as a silicon oxide film or asilicon oxynitride film (SiOxNy) is formed as an insulating film 770having an opening by a known process (sputtering method, LPCVD method,plasma CVD method, or the like). Then, a metallic element for promotingcrystallization is added to form a metallic containing layer 771. Plasmaprocessing, evaporation, a sputtering (method, ion implantation,solution coating, or the like is preferably used as a method (ofintroducing the above-mentioned metallic element into the semiconductorfilm. First thermal treatment is performed to crystallize thesemiconductor film. Since the heating time and the heating temperatureare dependent on the semiconductor film and the metallic element to beadded, those are preferably determined as appropriate by an operator. Inthis embodiment, it is exposed at 550° C. in an nitrogen atmosphere for4 hours.

Subsequently, first doping processing is performed to selectivelyintroduce an impurity element into the semiconductor film. According tothe doping processing, one kind or plural kinds of elements selectedfrom noble as elements is introduced into the semiconductor film by anion doping method, an ion implantation method, or the like. Also, onekind or plural kinds of elements selected from noble (as elements and animpurity element for providing an n-type or an impurity element forproviding a p-type may be introduced. One kind or plural kinds ofelements selected from noble gas elements, an impurity element forproviding an n-type, and an impurity element for providing a p-type maybe introduced. In addition, hydrogen may be added. In this embodiment,first, only argon is implanted at an accelerating voltage of 90 keV anda dose of 2×10¹⁵/cm² by an ion doping method.

Then, second thermal treatment is performed to move the metallic elementused for promoting crystallization to a region 772 into which theimpurity, element is introduced (gettering). In this embodiment, thermaltreatment is performed for gettering in a nitrogen atmosphere at 550° C.for 4 hours. (FIG. 20B)

The insulating film 770 and apart of the semiconductor film are etchedto form a semiconductor layer 773. Then, an insulating film includingsilicon such as a silicon oxide film or a silicon oxynitride film(SiOxNy) is formed as an insulating film 774 a by a known process(sputtering method, LPCVD method, plasma CVD method, or the like).

Subsequently, a conductive film 775 is formed. A material of theconductive film is not limited to a specific material. However, theconductive film may be made of an element selected from the groupconsisting of Ta, W, Ti, Mo, Al, Cu, Cr, and Nd, an alloy materialincluding mainly the above-mentioned element, or a compound materialincluding mainly the above-mentioned element. A semiconductor filmrepresented by a crystalline silicon film doped with an impurity elementsuch as phosphorus may be used as the conductive film. An AgPdCu alloymay be also used. Of course, the conductive film may be made from notonly a single layer but also a laminate. In this embodiment, theconductive film 775 made from a W film having a film thickness of 400 nmis formed. (FIG. 20C)

Subsequently, etching is performed to form a gate electrode 776 in whichtapers are formed in its end portions. A mask (not shown) made of aresist is formed by a photolithography method and etching processing isperformed for forming an electrode and a wiring. In the above etchingprocessing, when a shape of the mask made of a resist is suitable, theend portions of the conductive layer becomes taper shapes by an effectof the bias voltage applied to the substrate side. An angle of the taperportions becomes 15° to 45° Reference numeral 774 b denotes a (ateinsulating film. A region which is not covered with the gate electrode776 is etched at about 20 nm to 50 nm to form a thinner region.

Then, second doping processing is performed for impurity elementintroduction. According to the doping processing, an impurity, elementfor providing an n-type or an impurity element for providing a p-type isintroduced into the semiconductor film by an ion doping method, an ionimplantation method, or the like. By the doping processing, regions 777into which the impurity element is introduced at a high concentration,regions 778 into which the impurity element is introduced at a lowconcentration by the tapers in the end portions of the gate electrode,and a region (channel forming region) 779 into which the impurityelement is not introduced are formed. In this embodiment, phosphorus isused as an impurity element for providing an n-type. With respect to animplantation condition of phosphorus, 5% PH₃ diluted with hydrogen isused, an accelerating voltage is set to be 80 keV, and a dose is set tobe 1.5×10¹⁵/cm². A time required for implantation is about 8 minutes,and thus phosphorus can be implanted into the crystalline semiconductorfilm at an average concentration of 2×10²⁰/cm³. (FIG. 20D)

Then, the recovery of crystallinity of the region into which theimpurity element is introduced and the activation of the impurityelement are performed by the method shown in FIG. 3, which is describedin Embodiment 1.

Here, the reflector 312 may be a substrate such that a metallic film isformed on the surface thereof (reflecting surface of laser light) or maybe a reflecting plate made of a material having high reflectance. Inthis case, any material may be used for the metallic film. Typically, ametallic film including any element selected from the group consistingof aluminum, silver, tungsten, titanium, and tantalum is used.

Further, since the heater 103 and the heater controller 104 are includedin the stage 102 of the laser irradiation apparatus, it is possible toirradiate the laser light while heating the substrate to 100 to 450° C.and the recovery of crystallinity and the activation of the impurityelement can be performed with higher efficiency.

[Embodiment 4]

In this embodiment, the case where laser annealing is performed to asemiconductor film substrate obtained through manufacturing, stepsdifferent from Embodiment 1 to Embodiment 3 will be described.

First, a method of performing steps up to formation of the gateelectrode of a TFT will be described using FIGS. 23A to 23D. A glasssubstrate, a synthetic quartz glass substrate, a crystallized glasssubstrate, or a plastic substrate is used as a translucent substrate300. In this embodiment, a synthetic quartz glass substrate is used asthe translucent substrate 300.

A conductive film 780 having a desired shape is formed by forming aconductive film and performing etching. A material of the conductivefilm is not limited to a specific material. However, the conductive filmmay be made of an element selected from the group consisting of Ta, W,Ti, Mo, Al, Cu, Cr, and Nd, an alloy material including mainly theabove-mentioned element, or a compound material including mainly theabove-mentioned element. A semiconductor film represented by acrystalline silicon film doped with an impurity element such asphosphorus may be used as the conductive film. An AgPdCu alloy may bealso used. Of course, the conductive film may have not only a singlelayer structure but also a laminate structure. In this embodiment, theconductive film 780 made from a W film having a film thickness of 400 nmis formed. The W film is formed by a sputtering method using W as atarget. In addition, a thermal CVD method using, tungsten fluoride (WF₆)can also form the W film.

Then, an insulating film containing silicon such as a silicon oxide filmor a silicon oxynitride film (SiOxNy), which is formed by a known means(sputtering method, LPCVD method, plasma CVD method, or the like) ispreferably used as an insulating film 781. Of course, the insulatingfilm may have not only single layer structure but also a laminatestructure. In this embodiment, a silicon oxide film having a filmthickness of 150 nm is formed by a plasma CVD method.

Subsequently, a semiconductor film 782 having an amorphous structure isformed at a thickness of 25 to 80 nm (preferably, 30 to 60 nm) by aknown process (sputtering method, LPCVD method, plasma CVD method, orthe like). A material of the semiconductor film is not limited to aspecific material. However, the semiconductor film is preferably made ofsilicon, a silicon germanium (SiGe) alloy, or the like. In thisembodiment, an amorphous silicon film is formed at a film thickness of50 nm by a plasma CVD method. Then, a known crystallization method isperformed to crystallize the semiconductor film. In this embodiment, anickel acetate aqueous solution (5 ppm in weight conversionconcentration and 5 ml in volume) is applied onto the surface of theamorphous silicon film by a spin coat method to form a metalliccontaining layer 783. After that, it is exposed at 550° C. in annitrogen atmosphere for 4 hours. Since the heating time and the heatingtemperature vary depending on the kind of the semiconductor film and themetallic element to be added, those are preferably determined asappropriate by an operator. (FIG. 23A)

Subsequently, a mask 784 is formed and doping is performed toselectively introduce an impurity element into the semiconductor film.According to the doping processing, one kind or plural kinds of elementsselected from noble gas elements and an impurity element for providingan n-type or an impurity element for providing a p-type are introducedinto the semiconductor film by an ion dope method, an ion implantationmethod, or the like. Also, one kind or plural kinds of elements selectedfrom noble gas elements, an impurity element for providing an n-type,and an impurity element for providing a p-type may be introduced. Inaddition, hydrogen may be further added. In this embodiment, phosphorusis used as an impurity element for providing an n-type and argon is usedas a noble gas element. With respect to an implantation condition ofphosphorus, 5% PH₃ diluted with hydrogen is used, an acceleratingvoltage is set to be 80 keV, and a dose is set to be 1.5×10¹⁵/cm². Atime required for implantation is about 8 minutes and phosphorus can beimplanted into the crystalline semiconductor film at an averageconcentration of 2×10²⁰/cm³. On the other hand, argon is implanted at anaccelerating voltage of 90 keV and a dose of 2×10¹⁵/cm².

When the metallic element is used for crystallizing the semiconductorfilm as in this embodiment, it is desirable that the thermal treatmentis performed for gettering the metallic element. The metallic element ismoved from the channel forming region 786 to the regions 785 to whichthe impurity element is added by the thermal treatment and thus thechannel forming region 786 can be produced as a high resistance region.In this embodiment, thermal treatment is performed for gettering in anitrogen atmosphere at 550° C. for 4 hours.

The mask 784 is removed and the semiconductor layer as the active region787 is formed (FIG. 23C). After that, in order to sufficiently recovercrystallinity of the region into which the noble gas element isintroduced, laser annealing is performed as in Embodiments 1 to 3 (FIG.23D).

Here, the reflector 312 may be a substrate such that a metallic film isformed on the surface thereof (reflecting surface of laser light) or maybe a reflecting plate made of a material having high reflectance. Inthis case, any metallic material may be used for the metallic film.Typically, a metallic film including any element selected from the groupconsisting of aluminum, silver, tungsten, titanium, and tantalum isused.

Then, the laser light linearly processed through the optical system 201(in the drawings, only the cylindrical lens 207 is shown) describedusing, FIGS. 2A and 2B is irradiated from not only the front side butalso the rear side to the semiconductor film. When such an irradiationmethod is applied, since the conductive layer 780 has high thermalconductivity, heat generated by laser annealing can be easily diffused.Thus, when laser light is irradiated from not only the front side of thesubstrate but also the rear side thereof, the laser annealing can beeffectively performed.

Further, since the heater 103 and the heater controller 104 are includedin the stage 102 of the laser irradiation apparatus, it is possible toirradiate the laser light while heating the substrate to about 450° C.and the recovery of crystallinity and the activation of the impurityelement can be performed with higher efficiency.

[Embodiment 5]

In this embodiment, a method of manufacturing an active matrix substratewill be described using FIGS. 8A to 8C, 9A to 9C, 10A to 10C, 11 and 12.

First, in this embodiment, a substrate 320 made of glass such as bariumborosilicate glass (represented by #7059 glass, #1737 glass, or thelike, which is produced by Corning Corporation) or aluminoborosilicateglass is used. Note that a quartz substrate, a flexible substrate, orthe like can be used as the substrate 320. The flexible substrate is afilm substrate made of PET, PES, PEN, acrylic, or the like. When asemiconductor device is manufactured using the flexible substrate,weight reduction can be expected. It is preferred that a barrier layersuch as an aluminum film (AlON, AlN, AlO, or the like), a carbon film(DLC (diamond-like carbon) or the like), or an SiN film is formed as asingle layer or a multilayer on the surface of the flexible substrate oron both surfaces thereof to improve the durability and the like. Also, aplastic substrate having a heat resistance to a processing temperaturein this embodiment may be used.

Next, a base film 321 made from an insulating film such as a siliconoxide film, a silicon nitride film, or a silicon oxynitride film isformed on the substrate 320. In this embodiment, a two-layer structureis used for the base film 321. However, a single layer film of theinsulating film or a structure in which two layers or more are laminatedmay be used. As a first layer of the base film 321, a silicon oxynitridefilm 321 a is formed at 10 nm to 200 nm (preferably, 50 nm to 100 nm) bya plasma CVD method using SiH₄, NH₃, and N₂O as reactive gases. In thisembodiment, the silicon oxynitride film 321 a (composition ratio:Si=32%, O=27%, N=24%, and H=17%) having a film thickness of 50 nm isformed. As a second layer of the base film 321 a silicon oxynitride film321 b is laminated thereon at a thickness of 50 nm to 200 nm(preferably, 100 nm to 150 nm) by a plasma CUD method using SiH₄, andN₂O as reactive gases. In this embodiment, the silicon oxynitride film321 b (composition ratio: Si=32%, O=59%, N=7%, and H=2%) having a filmthickness of 100 nm is formed.

Then, a semiconductor film 322 is formed on the base film. Thesemiconductor film 322 is obtained by forming a semiconductor filmhaving, an amorphous structure at a thickness of 25 nm to 200 nm,preferably, 25 nm to 80 nm (typically, 30 nm to 60 nm) by a knownprocess (sputtering method, LPCVD method, plasma CVD method, or thelike). A material of the semiconductor film is not limited to a specificmaterial. However, the semiconductor film is preferably made of silicon,a silicon germanium (SiGe) alloy, or the like. Subsequently, a thermalcrystallization method using a catalyst such as nickel is performedthrough forming a metal containing layer 323. Of course, other knowncrystallization processing (laser crystallization method, thermalcrystallization method, or the like) may be combined with the thermalcrystallization method using a catalyst such as nickel (FIG. 8A). Acrystalline semiconductor film obtained by such a method is patterned ina predetermined shape to form semiconductor layers 402 to 406. In thisembodiment, after an amorphous silicon film having a thickness of 55 nmis formed by a plasma CVD method, a solution containing nickel is heldon the amorphous silicon film. The amorphous silicon film isdehydrogenated at 500° C. for 1 hour and then thermal treatment isperformed at 550° C. for 4 hours to form a crystalline silicon film.Then, the crystalline silicon film is patterned by using aphotolithography method to form the semiconductor layers 402 to 406.

When a laser crystallization method is also applied to thecrystallization of the semiconductor film, a solid laser, a gas laser, ametallic laser or the like, which is a pulse oscillation type or acontinuous light emitting (continuous wave) type, can be used. Note thatthere are exemplified a YAG laser, a YVO₄ laser, a YLF laser, a YAlO₃laser, a glass laser, a ruby laser, an alexandrite laser, a Ti:sapphirelaser, and the like, which perform continuous oscillation or pulseoscillation, as the solid laser. Also, there are exemplified an excimerlaser, an Ar laser, a Kr laser, a CO₂ laser, and the like, which performcontinuous oscillation or pulse oscillation, as the gas laser. Further,there are exemplified a helium cadmium laser, a copper vapor laser, anda gold vapor laser as the metallic laser. When these lasers are used, amethod of linearly condensing a laser beam emitted form a laseroscillator by an optical system and irradiating it to the semiconductorfilm is preferably used. A crystallization condition is selected asappropriate by an operator. When an excimer laser is used, a pulseoscillation frequency is set to be 300 Hz and a laser energy density isset to be 100 mJ/cm² to 1200 mJ/cm², preferably 100 mJ/cm² to 800 mJ/cm²(typically, 200 mJ/cm² to 700 mJ/cm²). When a YAG laser is used, it isdesirable that the second harmonic is used, a pulse oscillationfrequency is set to be 1 Hz to 300 Hz and a laser energy density is setto be 300 mJ/cm² to 1500 mJ/cm², preferably, 300 mJ/cm² to 1000 mJ/cm²(typically, 350 mJ/cm² to 800 mJ/cm²). A laser beam linearly condensedat a width of 100 μm to 1000 μm, for example, 400 μm is irradiated ontothe entire surface of the substrate. At this time, an overlap ratio ofthe linear laser beam may be set to be 50% to 98%. When a continuousoscillation laser is used, an energy density of about 0.01 MW/cm² to 100MW/cm² (preferably, 0.1 MW/cm² to 10 MW/cm²) is required. A stage ismoved relatively to laser light at a speed of about 0.5 cm/s to 2000cm/s and laser light is irradiated thereto to form the crystallinesilicon film.

After the formation of the semiconductor layers 402 to 406, a traceimpurity element (boron or phosphorus) may be doped for controlling athreshold value of a TFT.

Then, a gate insulating film 407 covering the semiconductor layers 402to 406 is formed. An insulating film containing silicon is formed as theKate insulating film 407 at a thickness of 40 nm to 150 nm by a plasmaCVD method or a sputtering method. In this embodiment, a siliconoxynitride film (composition ratio: Si=32, O=59%, N=7%, and H=2%) isformed at a thickness of 110 nm by a plasma CVD method. Of course, thegate insulating film is not limited to the silicon oxynitride film andanother insulating film containing silicon may be used as a siliconlayer or a laminate structure.

Also, when a silicon oxide film is used, TEOS (tetraethyl orthosilicate)and O₂ are mixed by a plasma CVD method, a reactive pressure is set tobe 40 Pa, and a substrate temperature is set to be 300° C. to 400° C.Then, discharge is caused at a high frequency (13.56 MHz) power densityof 0.5 W/cm² to 0.8 W/cm² and this the silicon oxide film can be formed.After that, when thermal anneal is performed for the thus formed siliconoxide film at 400° C. to 500° C., a preferable characteristic as to thegate insulating film can be obtained.

Then, as shown in FIG. 8B, a first conductive film 408 having, a filmthickness of 20 nm to 100 nm and a second conductive film 409 having afilm thickness of 100 nm to 400 nm are laminated on the gate insulatingfilm 407. In this embodiment, the first conductive film 408 made from aTaN film having a film thickness of 30 nm and the second conductive film409 made of a W film having a film thickness of 370 nm are laminated.The TaN film is formed by a sputtering method using Ta as a target in anatmosphere containing nitrogen. Also, the W film is formed by asputtering method using W as a target. In addition, it can be formed bya thermal CVD method using tungsten hexafluoride (WF₆). In any case,when these films are used for a gate electrode, it is necessary toreduce the resistance and resistivity of the W film is desirably made tobe 20 μΩcm or lower. When a crystal grain is enlarged, the resistivityof the W film can be reduced. However, if a large number of impurityelements such as oxygen are present in the W film, crystallization ishindered and the resistance is increased. Therefore, in this embodiment,the W film is formed by a sputtering method using high purity W (purityof 99.9999%) as a target after due consideration such that an impurityis not entered from a gas phase at film formation. Thus the resistivityof 9 μΩcm to 20 μΩcm can be realized.

Note that, in this embodiment, TaN is used for the first conductive film408 and W is used for the second conductive film 409. However, thematerial are not particularly limited to these and respective conductivefilms may be made of an element selected from the group consisting ofTa, W, Ti, Mo, Al, Cu, Cr, and Nd, an alloy material containing mainlythe above element, or a compound material containing mainly the aboveelement. A semiconductor film represented by a crystalline silicon filmdoped with an impurity element such as phosphorus may be also used. AnAgPdCu alloy may be also used. There may be also used a combination inwhich the first conductive film is made from a tantalum (Ta) film andthe second conductive film is made from a W film, a combination in whichthe first conductive film is made from a titanium nitride (TiN) film andthe second conductive film is made from a W film, a combination in whichthe first conductive film is made from a tantalum nitride (TaN) film andthe second conductive film is made from an Al film, and a combination inwhich the first conductive film is made from a tantalum nitride (TaN)film and the second conductive film is made from a Cu film.

Then, masks 410 to 415 made of resists are formed by a photolithographymethod and first etching processing is performed for forming anelectrode and a wiring. The first etching processing is performed undera first etching condition and a second etching condition. In thisembodiment, with respect to the first etching condition, an ICP(inductively coupled plasma) etching method is used, CF₄, Cl₂, and 02are used as etching gases, and a ratio of respective gas flow rates isset to be 25:25:10 (sccm). RF power having 500 W and 13.56 MHz issupplied to a coil type electrode at a pressure of 1 Pa to produceplasma and to thus perform etchings. Here, a dry etching apparatus(Model E645-□ICP) using ICP, which is produced by Matsushita Electronicindustrial Co., Ltd. is used. Also, RF power having 150 W and 13.56 MHzis supplied to a substrate side (sample stage) to apply a substantiallynegative self bias voltage. The W film is etched under the first etchingcondition to form end portions of the first conductive layer in tapershapes.

After that, the first etching condition is changed to the second etchingcondition without removing the masks 410 to 415 made of resists. CF₄ andCl₂ are used as etching gases and a ratio of respective gas flow ratesis set to be 30:30 (sccm). RF power having 500 W and 13.56 MHz issupplied to a coil type electrode at a pressure of 1 Pa to produceplasma and to thus perform etching for about 30 seconds. Also, RF powerhaving 20 W and 13.56 MHz is supplied to a substrate side (sample stage)to apply a substantially negative self bias voltage. In the secondetching condition such as CF₄ and Cl₂ are mixed, both the W film and theTaN film are etched to the same degree. Note that, in order to performetching without leaving the residue on the gate insulating film, anetching time is preferably increased at a rate by about 10% to 20%.

In the first etching processing, when shapes of the masks made ofresists are suitable, the end portions of the first and secondconductive layers become taper shapes by an effect of the bias voltageapplied to the substrate side. An angle of the taper portions becomes15° to 45°. Thus, first shaped conductive layers 417 to 422 made fromthe first conductive layers and the second conductive layers (firstconductive layers 417 a to 422 a and second conductive layers 417 b to422 b) are formed by the first etching processing. Reference numeral 416denotes a gate insulating film. Regions which are not covered with thefirst shaped conductive layers 417 to 422 are etched by about 20 nm to50 nm to form thinner regions. (FIG. 8D)

Then, first doping processing is performed without removing the masksmade of resists to add an impurity element for providing an n-type and anoble gas element for gettering the metallic element used for promotingcrystallization to the semiconductor layers (FIG. 9A). The dopingprocessing is preferably performed by an ion dope method or an ionimplantation method. With respect to a condition of the ion dope method,a dose is set to be 1×10¹³/cm² to 5×10¹⁵/cm² and an accelerating voltageis set to be 60 keV to 100 keV. In this embodiment, a dose is set to be1.5×10¹⁵/cm² and an accelerating voltage is set to be 80 keV. An elementbelonging to group 15 in the periodic table, typically, phosphorus (P)or arsenic (As) is used as the impurity, element for providing ann-type. Here, phosphorus (P) is used. Also, argon is used as the noblegas element. In this case, the conductive layers 417 to 421 become masksto the impurity element for providing an n-type and thus first highconcentration impurity regions 306 to 310 are formed in a selfalignment. The impurity element for providing an n-type is added to thefirst high concentration impurity regions 306 to 310 at a concentrationrange of 1×10²⁰/cm³ to 1×10²¹/cm³. On the other hand, argon is implantedat an accelerating voltage of 90 keV and a dose of 2×10¹⁵/cm².

Then, second etching processing is performed without removing the masksmade of resists. Here, SF₄, Cl₂, and O₂ are used as etching gases andthe W film is selectively etched. At this time, second conductive layers428 h to 433 b are formed by the second etching processing. On the otherhand, the first conductive layers 417 a to 422 a are not almost etched(428 a-433 a) to form second shaped conductive layers 428 to 433.

Then, as shown in FIG. 9B, second doping processing is performed withoutremoving the masks made of resists. In this case, a dose is decreased ascompared with the first doping processing and the impurity element forproviding an n-type is introduced at a high accelerating voltage of 70keV to 120 keV. In this embodiment, a dose is set to be 1.5×10¹⁴/cm² andan accelerating voltage is set to be 90 keV. According to the seconddoping processing, the second shaped conductive layers 428 to 433 areused as masks and the impurity element is also introduced into thesemiconductor film located under the second conductive layers 428 b to433 b to form second high concentration impurity regions 423 a to 427 aand low concentration impurity regions 423 b to 427 b.

Then, after the masks made of resists are removed, masks 434 a and 434 bmade of resists are newly formed and third etching processing isperformed as shown in FIG. 9C. SF₆ and Cl₂ are used as etching gases anda ratio of respective gas flow rates is set to be 50:10 (sccm). RF powerhaving 500 W and 13.56 MHz is supplied to a coil type electrode at apressure of 1.3 Pa to produce plasma and to thus perform etching forabout 30 seconds. Also, RF power having 10 W and 13.56 MHz is suppliedto a substrate side (sample stage) to apply a substantially negativeself bias voltage. Thus, the TaN films for a p-channel TFT and a TFT(pixel TFT) of a pixel portion are etched by the third etchingprocessing to form third shaped conductive layers 435 to 438 (435 a-438a and 435 b-438 b).

Then, after the masks made of resists are removed, the second shapedconductive layers 428 and 430 and the second shaped conductive layers435 to 438 are used as masks and the gate insulating film 416 isselectively removed to form insulating films 439 to 444 (FIG. 10A).

Then, new masks 445 a to 445 c made of resists are newly formed andthird doping processing is performed. By this third doping processing,impurity regions 446 a to 446 c and 447 a to 447 c to which an impurityelement for providing a conductivity type reverse to the aboveconductivity type is added are formed in the semiconductor layer as anactive layer of a p-channel TFT. The second conductive layers 435 a to438 a are used as masks to the impurity element and the impurity elementfor providing a p-type is added to form the impurity regions in a selfalignment. In this embodiment, the impurity regions 446 a to 446 c and447 a to 447 c are formed by an ion dope method using diborane (B₂H₆)(FIG. 10B). At the third doping processing, the semiconductor layercomposing an n-channel TFT is covered with the masks 445 a to 445 c madeof resists. Phosphorus is added to the impurity regions 446 a to 446 cand 447 a to 447 c at different concentrations by the first dopingprocessing and the second doping processing. However, doping isperformed such that a concentration of the impurity element forproviding a p-type in any region becomes 2×10²⁰/cm³ to 2×10²¹/cm³. Thus,since those impurity regions function as the source region and the drainregion of the p-channel TFT, no problem is caused. In this embodiment,since a portion of the semiconductor layer as the active layer of thep-channel TFT is exposed, there is an advantage such that the impurityelement (boron) can be easily added.

The impurity regions are formed in the respective semiconductor layersby the above steps.

Then, the masks 445 a to 445 c made of resists are removed and a firstinterlayer insulating film 461 is formed. An insulating film containingsilicon is formed as the first interlayer insulating film 461 at athickness of 100 nm to 200 nm by a plasma CVD method or a sputteringmethod. In this embodiment, a silicon oxynitride film is formed at afilm thickness of 150 nm by a plasma CVD method. Of course, the firstinterlayer insulating film 461 is not limited to the silicon oxynitridefilm and another insulating film including silicon may be used as asingle layer or a laminate structure.

Then, as shown in FIG. 10C, thermal treatment is performed for therecovery of crystallinity of the semiconductor layers and the activationof the impurity, element added to the respective semiconductor layers.This thermal treatment is performed by a thermal anneal method using afurnace-annealing furnace. The thermal anneal method may be performed atan oxygen concentration of 1 ppm or less, preferably, 0.1 ppm or less ina nitrogen atmosphere at 400° C. to 700° C., typically, 500° C. to 550°C. In this embodiment, the thermal treatment at 550° C. for 4 hours isperformed for the activation processing. Note that, a laser annealingmethod or a rapid thermal annealing method (RTA method) other than thethermal annealing method can be applied.

Note that, in this embodiment, the impurity regions 423 a, 425 a, 426 a,446 a, and 447 a including high concentration phosphorus arecrystallized by nickel used as a catalyst at crystallization,simultaneous to the above activation processions. Therefore, themetallic element is gettered into the impurity regions and a nickelconcentration in the semiconductor layers mainly serving as the channelforming regions is reduced. With respect to the TFT having the thusformed channel forming region, an off current value is reduced and ahigh field effect mobility is obtained because of high crystallinity.Thus, a preferable characteristic can be achieved.

Thermal treatment may be performed before the formation of the firstinterlayer insulating film. Note that, when the wiring material used isvulnerable to heat, it is preferable that thermal treatment is performedafter the interlayer insulating film (insulating film including mainlysilicon, for example, silicon nitride film) for protecting a wiring andthe like is formed as in this embodiment.

In order to perform satisfactory recovery of crystallinity of theregions into which the noble gas element is introduced and theactivation of the impurity element, laser light irradiated from thefront side of the substrate is reflected by a reflector 340 provided inthe rear side of the substrate. Thus, the laser light is irradiated fromthe rear side of the substrate (FIG. 10C). In this embodiment, analuminum plate is used as the reflector 340 for irradiating laser lightto the substrate at a slant angle. Simultaneously, when a heater or thelike is used and thermal treatment is also performed from the rear sideof the substrate, hydrogenation processing using hydrogen included inthe first interlayer insulating film can be performed.

When a trace impurity element (boron or phosphorus) is doped forcontrolling a threshold of a TFT, the crystallinity of the channelforming region is sufficiently recovered by the laser light irradiationfrom the rear side.

When thermal treatment is not simultaneously performed in a laserannealing step, it is desirable that thermal treatment is performed inan atmosphere including, 3% to 100% of hydrogen at 300° C. to 550° C.for 1 hour to 12 hours to hydrogenate the semiconductor layers. In thisembodiment, thermal treatment is performed in a nitrogen atmosphereincluding about 3% of hydrogen at 410° C. for 1 hour. This step is astep of terminating, dangling bonds of the semiconductor layers byhydrogen included in the interlayer insulating film. Plasmahydrogenation (using hydrogen excited by plasma) may be performed asanother hydrogenation means.

Then, a second interlayer insulating film 462 made of an inorganicinsulating, film material or an organic insulator material is formed onthe first interlayer insulating film 461. In this embodiment, an acrylicresin film having a film thickness of 1.6 μm is formed. A materialhaving a viscosity of 10 cp to 1000 cp, preferably, 40 cp to 200 cp,such that an uneven surface is produced is used therefor.

In this embodiment, in order to prevent mirror reflection, an unevenportion is formed on the surface of a pixel electrode by forming thesecond interlayer insulating film 462 such that an uneven surface isproduced. In order to forming the uneven portion on the surface of thepixel electrode and thus to attain light scattering property, a convexportion may be formed in a region under the pixel electrode. In thiscase, since the convex portion can be formed using the same photo maskas in the formation of the TFT, it can be formed without increasing thenumber of steps. Note that the convex portion may be providedappropriately on the substrate in a pixel portion region except forwirings and TFTs. Thus, the uneven portion is formed on the surface ofthe pixel electrode along the uneven portion produced on the surface ofthe insulating film covering the convex portion.

A film having a flattened surface may be used as the second interlayerinsulating film 462. In this case, it is desirable that the unevenportion is produced on the surface by adding a step for a knownsandblast method, etchings method, or the like after the pixel electrodeis formed, and thus mirror reflection is prevented and whiteness isincreased by scattering reflected light.

Then, wirings 463 to 467 electrically connected with the respectiveimpurity regions are formed in a driver circuit 506. Note that thosewirings are formed by patterning a laminate film composed of a Ti filmhaving a film thickness of 50 nm and an alloy film (alloy film of Al andTi) having a film thickness of 500 nm.

Also, a pixel electrode 470, a gate wiring 469, and a connectionelectrode 468 are formed in a pixel portion 507 (FIG. 11). A sourcewiring 436 (laminate of layer 436 a and layer 436 b is electricallyconnected with the pixel TFT through the connection electrode 468. Thegate wiring 469 is electrically connected with the gate electrode of thepixel TFT. The pixel electrode 470 is electrically connected with adrain region 426 a of the pixel TFT and further with a semiconductorlayers 447 a and 447 b which serve as one electrode composing a storagecapacitor 505. It is desirable that a material having high reflectancesuch as a film including mainly Al or Ag or a laminate film thereof isused for the pixel electrode 470.

Thus, the driver circuit 506 having a CMOS circuit 509 composed of ann-channel TFT 501 and a p-channel TFT 502 and an n-channel TFT 503 andthe pixel portion 507 having a pixel TFT 504 and a storage capacitor 505can be formed on the same substrate. Therefore, the active matrixsubstrate is completed.

The n-channel TFT 501 in the driver circuit 506 includes a channelforming region 423 c, low concentration impurity regions 423 b (GOLDregions) overlapped with a first conductive layer 428 a composing aportion of the gate electrode, and high concentration impurity regions423 a which each serve as the source region or the drain region. Thep-channel TFT 502 which is connected with the n-channel TFT 501 throughan electrode 466 and composes the CMOS circuit includes a channelforming region 446 d, impurity regions 446 b and 446 c formed outsidethe gate electrode, and high concentration impurity regions 446 a whicheach serve as the source region or the drain region. Also, the n-channelTFT 503 includes a channel forming region 425 c, low concentrationimpurity regions 425 h (GOLD regions) overlapped with a first conductivelayer 430 a composing a portion of the gate electrode, and highconcentration impurity regions 425 a which each serve as the sourceregion or the drain region.

The pixel TFT 504 in the pixel portion includes a channel forming region426 c, low concentration impurity regions 426 b (LDD regions) formedoutside the gate electrode, and high concentration impurity regions 426a which each serve as the source region or the drain region. Impurityelements for providing a p-type are added to respective semiconductorlayers 447 a and 447 h which serve as one electrode of the storagecapacitor 505. The storage capacitor 505 is composed of an electrode(laminate of the layer 438 a and the layer 438 h), and semiconductorlayers 447 a to 447 c using the insulating film 444 as dielectric.

Also, according to a pixel structure of this embodiment, in order tolight-shield a gap between pixel electrodes without using a blackmatrix, the pixel electrode is formed and located such that end portionsthereof are overlapped with the source wiring.

FIG. 12 is a top view of a pixel portion on the active matrix substratemanufactured in this embodiment. Note that the same reference numeralsare used for portions corresponding to those of FIG. 8A to FIG. 11. Thedashed line A-A′ in FIG. 11 corresponds to a cross sectional viewobtained by cutting along the dashed line A-A′ of FIG. 12. Also, thedashed line B-B′ in FIG. 11 corresponds to a cross sectional viewobtained by cutting along the dashed line B-B′ of FIG. 12.

[Embodiment 6]

In this embodiment, an explanation will be given as follows of steps offabricating a reflection type liquid crystal display apparatus from theactive matrix substrate fabricated in Embodiment 5. FIG. 13 is used inthe explanation.

First, in accordance with Embodiment 5, there is provided the activematrix substrate in the state of FIG. 11 and thereafter, an alignmentfilm 567 is formed above the active matrix substrate of FIG. 11, atleast above the pixel electrode 470 and a rubbing processing is carriedout. Further, in this example, before forming the alignment film 567, bypatterning an organic resin film such as an acrylic resin film, spacersin a columnar shape 572 are formed at desired positions in order tomaintain an interval between substrates. Further, in place of thespacers in the columnar shape, spacers in a spherical shape may bescattered over an entire face of the substrate.

Next, an opposed substrate 569 is prepared. Successively, there areformed color layers 570 and 571 and a flattening film 573. A lightshielding portion is formed by overlapping the color layer 570 of redcolor and the color layer 571 of blue color. Further, the lightshielding portion may be formed by overlapping, portions of a colorlayer of red color and a color layer of green color.

In this embodiment, there is used the substrate shown in Embodiment 5.Therefore, in FIG. 12 showing the top view of the pixel portion ofEmbodiment 5, it is necessary to shield at least a gap between the gatewiring 469 and the pixel electrode 470, a gap between the gate wiring469 and the connection electrode 468 and a gap between the connectionelectrode 468 and the pixel electrode 470. In this embodiment, therespective color layers are arranged such that the light shieldingportions constituted by laminating the color layers overlap positions tobe shielded and the opposed substrate is pasted thereto.

A number of steps can be reduced by shielding the raps among therespective pixels by the light shielding portions constituted bylaminating the color layers in this way without forming light shieldinglayers such as black masks.

Next, the opposed electrode 576 constituted by a transparent conductivefilm is formed on the flattening film 573 at least at the pixel portion,an alignment film 574 is formed over an entire face of the opposedsubstrate and the rubbing processing is carried out.

Further, the active matrix substrate formed with the pixel portion andthe driver circuit and the opposed substrate are pasted together by aseal member 568. The seal member 568 is mixed with filler and two of thesubstrates are pasted together at a uniform interval therebetween by thefiller and the spacers in the columnar shape. Thereafter, the intervalbetween the two substrates is injected with a liquid crystal material575 and is completely sealed by a seal agent (not illustrated). Apublicly-known liquid crystal material may be used for the liquidcrystal material 575. In this way, the reflection type liquid crystaldisplay apparatus shown in FIG. 13 is finished. Further, as necessary,the active matrix substrate or the opposed substrate may be divided intoa desired shape. Further, a polarizer (not illustrated) is pasted toonly the opposed substrate. Further, FPC is pasted thereto by usingpublicly-known technology.

The liquid crystal display panel fabricated in this way can be used asdisplay portions of various electronic apparatus.

This embodiment can be freely combined with the structure in Embodiments1 to 5.

[Embodiment 7]

In this embodiment, a process for manufacturing an active matrix liquidcrystal display device different from that shown in Embodiment 6 usingthe active matrix substrate manufactured in Embodiment 5 will bedescribed. The description is made with reference to FIG. 21.

First, after the active matrix substrate with the state of FIG. 11 isobtained according to Embodiment 5, an orientation film (alignment film)1067 is formed on the active matrix substrate of FIG. 11 to perform arubbing process. Note that, in this embodiment, before the formation ofthe orientation film 1067, an organic resin film such as an acrylicresin film is patterned to form a columnar spacer for keeping a gapbetween substrates in a desired position. Also, instead of the columnarspacer, a spherical spacer may be distributed over the entire surface.

Next, an opposing substrate 1068 is prepared. A color filter in which acolored layer 1074 and a light shielding layer 1075 are arrangedcorresponding to each pixel is provided in this opposing substrate 1068.Also, a light shielding layer 1077 is provided in a portion of a drivercircuit. A leveling film 1076 for covering this color filter and thelight shielding layer 1077 is provided. Next, a counter electrode 1069made of a transparent conductive film is formed in a pixel portion onthe leveling film 1076, and then an orientation film 1070 is formed onthe entire surface of the opposing substrate 1068 to perform a rubbingprocess.

Then, the active matrix substrate in which the pixel portion and thedriver circuit are formed and the opposing substrate are adhered to eachother by using a sealing member 1071. Filler is mixed with the sealingmember 1071, and two substrates are adhered to each other with a uniforminterval by this filler and the columnar spacer. After that, a liquidcrystal material 1073 is injected into a space between both substratesand then completely encapsulated by a sealing member (not shown). Aknown liquid crystal material may be used as the liquid crystal material1073. Thus, the active matrix liquid crystal display device as shown inFIG. 21 is completed. If necessary, the active matrix substrate or theopposing substrate is cut with a predetermined shape. Also, apolarization plate and the like are suitably provided using a knowntechnique. And, an FPC is adhered to the active matrix liquid crystaldisplay device using a known technique.

A structure of a liquid crystal display panel thus obtained can be usedas display portions of various electronic apparatus.

This embodiment can be freely combined with the structure in Embodiments1 to 5.

[Embodiment 8]

In this embodiment, an example in which a light emitting device ismanufactured according to the present invention will be described. Inthis specification, the light emitting device is a generic name for adisplay panel in which a light emitting element formed over a substrateis sealed between the substrate and a cover member and a display modulein which an IC is mounted on the display panel. Note that the lightemitting element has a layer (light emitting layer) including an organiccompound such that electro luminescence (EL) produced by applying anelectric field thereto is obtained, an anode layer, and a cathode layer.As the electro luminescence in the organic compound, there are lightemission (fluorescence) produced when it is returned from a singletexcitation state to a ground state and light emission (phosphorescence)produced when it is returned from a triplet excitation state to a groundstate. The electro luminescence includes either light emission or bothlight emissions.

FIG. 14 is a cross sectional view of a light emitting, device of thisembodiment. In FIG. 14, a switching TFT 603 provided in a pixel portion612 on a substrate 700 is made from the n-channel TFT 504. Thus, itsstructure will be described with reference to the description of then-channel TFT 504.

Note that, in this embodiment, a double gate structure in which twochannel forming regions are formed is used. However, a single gatestructure in which one channel forming region is formed or a triple gatestructure in which three channel forming regions are formed may be used.

A driver circuit 610 provided on the substrate 700 is made from the CMOScircuit shown in FIG. 14. Thus, its structure will be described withreference to the descriptions of the n-channel TFT 501 and the p-channelTFT 502. Note that a single gate structure is used in this embodiment.However, a double gate structure or a triple gate structure may be used.

Wirings 701 and 703 serve as source wirings of the CMOS circuit and awiring 702 serves as a drain wiring. Also, a wiring 704 serves as awiring for electrically connecting a source wiring 708 with the sourceregion of the switching TFT and a wiring 705 serves as a wiring forelectrically connecting a drain wiring 709 with the drain region of theswitching TFT.

Note that a current control TFT 604 is made from the p-channel TFT 502.Thus, its structure will be described with reference to the descriptionof the p-channel TFT 502. Note that a single gate structure is used inthis embodiment. However, a double gate structure or a triple gatestructure may be used.

A wiring 706 is a source wiring (corresponding to a current supply line)of the current control TFT 604. Reference numeral 707 denotes anelectrode electrically connected with a pixel electrode 710 byoverlapping it on the pixel electrode 710 of the current control TFT604.

Note that reference numeral 710 denotes the pixel electrode (anode of alight emitting element) made from a transparent conductive film. Acompound of indium oxide and tin oxide, a compound of indium oxide andzinc oxide, zinc oxide, tin oxide, or indium oxide can be used for thetransparent conductive film. Also, the transparent conductive film towhich gallium is added may be used. The pixel electrode 710 is formed ona flat interlayer insulating film 711 before the above wiring areformed. In this embodiment, it is very important to remove a step due tothe TFT using a planarizing film 711 made of a resin and thus toplanarize the surface. Since a light emitting layer formed later is verythin, there is the case where light emission failure is caused by thestep. Thus, it is desirable that the surface is flattened before theformation of the pixel electrode so that the light emitting layer mayhave its surface flattened as much as possible.

After the formations of the wirings 701 to 707, a hank 712 is formed asshown in FIG. 14. The bank 712 may be formed by patterning an insulatingfilm including silicon or an organic resin film, having a thickness of100 nm to 400 nm.

Note that since the bank 712 is an insulating film, the attention to anelectrostatic discharge damage of an element in film formation isrequired. In this embodiment, a carbon particle or a metallic particleis added into the insulating film as a material for the hank 712 toreduce the resistivity, and thus the generation of static electricity issuppressed. At this time, the amount of carbon particle or metallicparticle to be added is preferably controlled such that the resistivityis 1×10⁶ to 1×10¹² Ωm (preferably, 1×10⁵ to 1×10¹⁰ Ωm).

A light emitting layer 713 is formed on the pixel electrode 710. Notethat, although only one pixel is shown in FIG. 14, light emitting layerscorresponding to respective colors of R (red), G (green), and B (blue)are separately formed in this embodiment. Also, in this embodiment, alow molecular system organic light emitting material is formed by anevaporation method. Specifically, a laminate structure is used such thata copper phthalocyanine (CuPc) film having a thickness of 20 nm isprovided as a hole injection layer and a tris-8-quinolinolato aluminumcomplex (Alq₃) film having a thickness of 70 nm is provided thereon asthe light emitting layer. When a fluorescent coloring matter such asqluinacridon, perylene, or DCM1 is added to Alq₃, a light emitting colorcan be controlled.

Note that the above materials are examples of the organic light emittingmaterials which can be used for the light emitting layer and the presentinvention is not limited to these materials. The light emitting layer(layer for effecting light emission and carrier transfer therefor) maybe preferably formed by freely combining a light emitting layer, acharge transport layer, and a charge injection layer. For example, inthis embodiment, an example in which the low molecular system organiclight emitting material is used as the light emitting layer isdescribed. However, a middle molecular system organic light emittingmaterial or a polymer system organic light emitting material may beused. In this embodiment, an organic light emitting material which hasno sublimation property and in which the number of molecules is 20 orsmaller or a length of linked molecules is 10 μm or shorter is used asthe middle molecular system organic light emitting material. Withrespect to an example in which the polymer system organic light emittingmaterial is used, a laminate structure may be used such that apolythiophene (PEDOT) film having a thickness of 20 nm is provided asthe hole injection layer by a spin coating method and aparaphenylenevinylene (PPV) film having a thickness of about 100 nm isprovided thereon as the light emitting layer. When a π conjugate systempolymer of PPV is used, a light emitting wavelength from a red color toa blue color can be selected. An inorganic material such as siliconcarbide can be also used for the charge transport layer or the chargeinjection layer. Known materials can be used as the organic lightemitting material and the inorganic material.

Then, a cathode 714 made from a conductive film is provided on the lightemitting layer 713. In the case of this embodiment, an alloy film ofaluminum and lithium is used as the conductive film. Of course, a knownMgAg film (alloy film of magnesium and silver) may be used. A conductivefilm made of an element belonging to group 1 or group 2 of the periodictable or a conductive film to which the element is added may be used asa cathode material.

When the cathode 714 is formed, a light emitting element 715 iscompleted. Note that the light emitting element 715 described hereindicates a diode composed of the pixel electrode (anode) 710, the lightemitting layer 713, and the cathode 714.

It is effective to provide a passivation film 716 so as to completelycover the light emitting element 715. The passivation film 716 is madefrom an insulating film including a carbon film, a silicon nitride film,or a silicon oxynitride film and used as a single layer of theinsulating film or a laminate as a combination thereof.

At this time, a film having high coverage is preferably used as thepassivation film and it is effective to use a carbon film, particularly,a DLC (diamond-like carbon) film. Since the DLC film can be formed in atemperature range of a room temperature to 100° C., it can be easilyformed over the light emitting layer 713 having a low heat resistance.Also, the DLC film has a high blocking effect to oxygen and thus theoxidation of the light emitting layer 713 can be suppressed. Therefore,a problem such as the light emitting layer 713 is oxidized during asealing step followed by this step can be solved.

Further, a sealing member 717 is provided on the passivation film 716and a cover member 718 is bonded thereto. An ultraviolet curable resinmay be used as the sealing member 717 and it is effective provide amaterial having a moisture absorption effect or a material having ananti-oxidant effect in the inner portion. In this embodiment, a glasssubstrate, a quartz substrate, or a plastic substrate (including aplastic film), in which a carbon film (preferably, a diamond-like carbonfilm) is formed on both surfaces is used as the cover member 718.

Thus, a light emitting device having the structure as shown in FIG. 14is completed. Note that, it is effective that steps until thepassivation film 716 is formed after the formation of the bank 712 areperformed in succession without exposure to air by using a multi-chambersystem (or in-line system) film formation apparatus. Further, subsequentsteps up to bonding of the cover member 718 can be also performed insuccession without exposure to air.

Thus, n-channel TFTs 601 and 602, a switching TFT (n-channel TFT) 603,and a current control TFT (n-channel TFT) 604 are formed over thesubstrate 700. The number of masks required for manufacturing stepsuntil this point is smaller than that for a general active matrix lightemitting device.

That is, manufacturing steps of TFTs are greatly simplified and theimprovement of a yield and the reduction in a manufacturing cost can berealized.

Further, as described using FIG. 14, when the impurity regionsoverlapped with the gate electrode through the insulating film areprovided, the n-channel TFT resistant to deterioration caused due to ahot carrier effect can be formed. Thus, the light emitting device havinghigh reliability can be realized.

Also, in this embodiment, only the structures of the pixel portion andthe driver circuit are indicated. However, according to themanufacturing steps of this embodiment, logical circuits such as asignal separating circuit, a D/A converter, an operational amplifier, aγ correction circuit, and the like can be also formed on the sameinsulator. In addition, a memory and a microprocessor can be formed.

A light emitting device of this embodiment after a sealing (orenclosure) step for protecting the light emitting element is performedwill be described using FIGS. 15A and 15B. Note that reference symbolsused in FIG. 14 are referred to if necessary.

FIG. 15A is a top view indicating a state after the sealing of the lightemitting element and FIG. 15B is a cross sectional view obtained bycuttings FIG. 15A along the line C-C′. Reference numeral 801 indicatedby a dot line denotes a source side driver circuit, 806 denotes a pixelportion, and 807 denotes a gate side driver circuit. Also, referencenumeral 901 denotes a cover member, 902 denotes a first seal member, and903 denotes a second seal member. A sealing member 907 is provided inthe inside portion surrounded by the first seal member 902.

Note that reference numeral 904 denotes a wiring for transmittingsignals inputted to the source side driver circuit 801 and the gate sidedriver circuit 807. The wiring 904 receives a video signal and a clocksignal from an FPC (flexible printed circuit) 905 serving as an externalinput terminal. Although only the FPC is shown here, a printed wiringboard (PWB) may be attached to the FPC. The light emitting device inthis specification includes not only a main body of the light emittingdevice but also the light emitting device to which the FPC or the PWB isattached.

Next, the cross sectional structure will be described using FIG. 15B.The pixel portion 806 and the gate side driver circuit 807 are formedover the substrate 700. The pixel portion 806 is composed of a pluralityof pixels each including the current control TFT 604 and the pixelelectrode 710 electrically connected with the drain thereof. The gateside driver circuit 807 is composed of a CMOS circuit (see FIG. 14) inwhich the n-channel TFT 601 and the p-channel TFT 602 are combined witheach other.

The pixel electrode 710 serves as the anode of the light emittingelement. The banks 712 are formed in both ends of the pixel electrode710. The light emitting layer 713 and the cathode 714 of the lightemitting element are formed on the pixel electrode 710.

The cathode 714 also serves as a wiring common to all pixels and iselectrically connected with the FPC 905 through a connection wiring 904.All elements which are included in the pixel portion 806 and the gateside driver circuit 807 are cove red with the cathode 714 and apassivation film 716.

Also, the cover member 901 is bonded to the resultant substrate throughthe first seal member 902. Note that a spacer made from a resin film maybe provided to keep an interval between the cover member 901 and thelight emitting element. The sealing member 907 is filled inside thefirst seal member 902. An epoxy system resin is preferably used for thefirst seal member 902 and the sealing member 907. The first seal member902 is desirably made of a material that does not transmit moisture andoxygen as much as possible. A material having a moisture absorptioneffect or a material having an anti-oxidant effect may be included inthe inner portion of the sealing member 907.

The sealing member 907 provided so as to cover the light emittingelement also serves as an adhesive for bonding of the cover member 901.Also, in this embodiment, FRP (fiberglass-reinforced plastics), PVF(polyvinylfuroride), Mylar, polyester, or acrylic can be used as amaterial of the cover member 901.

Also, after bonding of the cover member 901 using the sealing member907, the second seal member 903 is provided so as to cover side surfaces(exposed surface) of the sealing member 907. The second seal member 903can be made of the same material as the first seal member 902.

With the above structure, when the light emitting element is sealed withthe sealing member 907, the light emitting element can be completelyshut from the outside and it can be prevented that a substance such asmoisture or oxygen which promotes deterioration due to oxidation of thelight emitting, layer is entered from the outside. Therefore, the lightemitting device having high reliability is obtained.

Note that this embodiment can be freely combined with Embodiments 1 to5.

[Embodiment 9]

In this embodiment, a light emitting device having a pixel structuredifferent from Embodiment 8 will be described. FIG. 22 is used for thedescription.

In FIG. 22, a TFT having the same structure as the n-channel TFT 504shown in FIG. 11 is used as a current control TFT 4501. Of course, thegate electrode of the current control TFT 4501 is electrically connectedwith a drain wiring of a switching TFT 4402. Also, the drain wiring ofthe current control TFT 4501 is electrically connected with a pixelelectrode 4504.

In this embodiment, the pixel electrode 4504 made from a conductive filmserves as the cathode of the light emitting element. Concretely, analloy film of aluminum and lithium is used. A conductive film made of anelement belonging to the group 1 or the group 2 of the periodic table ora conductive film to which the element is added is preferably used.

A light emitting layer 4505 is formed on the pixel electrode 4504. Notethat, although only one pixel is shown in FIG. 22, a light emittinglayer corresponding to G (green) is formed by an evaporation method anda coating method (preferably, a spin coating method) in this embodiment.Concretely, a laminate structure is used such that a lithium fluoride(LiF) film having a thickness of 20 nm is provided as an electroninjection layer and a PPV (polyparaphenylenevinylene) film having athickness of 70 nm is provided thereon as the light emitting layer.

Then, an anode 4506 made from a transparent conductive film is providedon the light emitting layer 4505. In the case of this embodiment, aconductive film made of a compound of indium oxide and tin oxide or acompound of indium oxide and zinc oxide is used as the transparentconductive film.

When the anode 4506 is formed, a light emitting element 4507 iscompleted. Note that the light emitting element 4507 described hereindicates a diode composed of the pixel electrode (cathode) 4504, thelight emitting layer 4505, and the anode 4506.

It is effective to provide a passivation film 4508 so as to completelycover the light emitting element 4507. The passivation film 4508 is madefrom an insulating film including a carbon film, a silicon nitride film,or a silicon oxynitride film and used as a single layer of theinsulating film or a laminate as a combination thereof.

Further, a sealing member 4509 is provided on the passivation film 4508and a cover member 4510 is bonded thereto. An ultraviolet curable resinis preferably used as the sealing member 4509 and it is effective toprovide a material having a moisture absorption effect or a materialhaving an anti-oxidant effect in the inner portion. In this embodiment,a glass substrate, a quartz substrate, or a plastic substrate (includinga plastic film), in which a carbon film (preferably, a diamond-likecarbon film) is formed on both surfaces is used as the cover member4510.

Note that this embodiment can be freely combined with Embodiments 1 to5.

[Embodiment 10]

The CMOS circuit and the pixel portion formed by implementing theinvention can be used in various electric devices (active matrix typeliquid crystal display, active matrix type EC display, active matrixtype light emitting display). That is, the present invention can beimplemented in all of electronic apparatuses integrated with theelectric devices at display portions thereof.

As such electronic apparatus, there are pointed out a video camera, adigital camera, a projector, a head mount display (goggle type display),a car navigation system, a car stereo, a personal computer, a portableinformation terminal (mobile computer, portable telephone or electronicbook) and the like. Examples of these are shown in FIG. 16A through 16F,FIG. 17A through 17D and FIG. 18A through 18C.

FIG. 16A shows a personal computer including a main body 3001, an imageinput portion 3002, a display portion 3003 and a keyboard 3004. Theinvention is applicable to the display portion 3003.

FIG. 16B shows a video camera including a main body 3101, a displayportion 3102, a voice input portion 3103, operation switches 3104, abattery 3105 and an image receiving portion 3106. The invention isapplicable to the display portion 3102.

FIG. 16C shows a mobile computer including a main body 3201, a cameraportion 3202, an image receiving portion 3203, an operation switch 3204and a display portion 3205. The invention is applicable the displayportion 3205.

FIG. 16D shows a goggle type display including a main body 3301, adisplay portion 3302 and an arm portion 3303. The invention isapplicable to the display portion 3302.

FIG. 16E shows a player using a record medium recorded with programs(hereinafter, referred to as record medium) including a main body 3401,a display portion 3402, a speaker portion 3403, a record medium 3404 andan operation switch 3405. The player uses DVD (Digital Versatile Disc)or CD as the record medium and can enjoy music, enjoy movie and carryout game or Internet. The invention is applicable to the display portion3402.

FIG. 16F shows a digital camera including a main body 3501, a displayportion 3502, an eye contact portion 3503, operation switches 3504 andan image receiving portion (not illustrated). The invention isapplicable to the display portion 3502.

FIG. 17A shows a front type projector including a projection apparatus3601 and a screen 3602. The invention is applicable to a liquid crystaldisplay apparatus 3808 constituting a portion of the projectionapparatus 3601 and other driver circuit.

FIG. 17B shows a rear type projector including a main body 3701, aprojection apparatus 3702, a mirror 3703 and a screen 3704. Theinvention is applicable to a liquid crystal display apparatus 3808constituting a portion of the projection apparatus 3702 and other drivercircuit.

Further, FIG. 17C is a view showing an example of a structure of theprojection apparatus 3601 and 3702 in FIG. 17A and FIG. 17B. Theprojection apparatus 3601 or 3702 is constituted by a light sourceoptical system 3801, mirrors 3802, and 3804 through 3806, a dichroicmirror 3803, a prism 3807, a liquid crystal display apparatus 3808, aphase difference plate 3809 and a projection optical system 3810. Theprojection optical system 3810 is constituted by an optical systemincluding a projection lens. Although the embodiment shows an example ofthree plates type, the embodiment is not particularly limited theretobut may be of, for example, a single plate type. Further, a person ofexecuting the embodiment may pertinently provide an optical system suchas an optical lens, a film having a polarization function, a film foradjusting a phase difference or an IR film in an optical path shown byarrow marks in FIG. 17C.

Further, FIG. 17D is a view showing an example of a structure of thelight source optical system 3801 in FIG. 17C. According to theembodiment, the light source optical system 3801 is constituted by areflector 3811, a light source 3812, lens arrays 3813 and 3814, apolarization conversion element 3815 and a focusing lens 3816. Further,the light source optical system shown in FIG. 17D is only all exampleand the embodiment is not particularly limited thereto. For example, aperson of executing the embodiment may pertinently provide an opticalsystem such as an optical lens, a film having a polarization function, afilm for adjusting a phase difference or an IR film in the light sourceoptical system.

However, according to the projectors shown in FIGS. 17A, 17B and 17C,there is shown a case of using a transmission type electronic apparatusand an example of applying a reflection type electronic apparatus is notillustrated.

FIG. 18A shows a portable telephone including a main body 3901, a voiceoutput portion 3902, a voice input portion 3903, a display portion 3904,an operation switch 3905 and an antenna 3906. The invention isapplicable to the display portion 3904.

FIG. 18B shows a portable book (electronic book) including a main body4001, display portions 4002 and 4003, a record medium 4004, an operationswitch 4005 and an antenna 4006. The invention is applicable to thedisplay portions 4002 and 4003.

FIG. 18C shows a display including a main body 4101, a support base 4102and a display portion 4103. The invention is applicable to the displayportion 4103. The display according to the invention is advantageousparticularly in the case of large screen formation and is advantageousin the display having a diagonal length of 10 inch or more(particularly, 30 inch or more).

As has been described, the range of applying the invention is extremelywide and is applicable to electronic apparatus of all the fields.Further, the electronic apparatus of the embodiment can be realized byusing any constitution comprising any combinations of Embodiments 1 to9.

When the structure of the present invention is used, the followingessential significance can be obtained.

(a) This is a simple structure that completely accords with aconventional TFT manufacturing process.

(b) The amount of impurity element to be introduced can be decreased.Thus, damage due to doping processing can be reduced in the gateinsulating film, the semiconductor film, and the interface therebetween.

(c) The crystallinity of the semiconductor film into which the impurityelement is introduced can be easily restored.

(d) The impurity element can be satisfactorily activated.

(e) The metallic element used for promoting crystallization can besatisfactorily removed.

(f) The width of the overlap regions between the gate electrode and thelow concentration impurity regions can be shortened. Thus, a transistorcan be further microfabricated.

(g) This is a method capable of manufacturing a TFT having a superiorelectrical characteristic obtained by attaining the above advantages.

1. A method of manufacturing a semiconductor device, said methodcomprising the steps of: forming a semiconductor film over a firstsurface of a translucent substrate; forming an insulating film on thesemiconductor film; forming a conductive film on the insulating film;introducing an impurity into the semiconductor film to form a channelforming region, at least a low concentration impurity region and atleast a high concentration impurity region; wherein the channel formingregion is overlapped with the conductive film; wherein the lowconcentration impurity region is overlapped with portion of theconductive film; wherein at least one selected from the group consistingof a source region and a drain region comprises the high concentrationimpurity region; irradiating with a first laser light from the firstsurface and with a second laser light from a second surface of thetranslucent substrate during heating the translucent substrate from thesecond surface to activate the impurity, wherein the second laser lightis a portion of the first laser light which is transmitted through thetranslucent substrate and reflected by a reflector; wherein thereflector is formed adjacent to the second surface of the translucentsubstrate.
 2. A method of manufacturing a semiconductor device, saidmethod comprising the steps of: forming a first semiconductor film overa first surface of a translucent substrate; introducing a metal elementinto the first semiconductor film; first heating the first semiconductorfilm to form a second semiconductor film; forming an insulating film onthe second semiconductor film; forming a conductive film on theinsulating film; introducing an impurity into the second semiconductorfilm to form a channel forming region, at least a low concentrationimpurity region and at least a high concentration impurity region;wherein the channel forming region is overlapped with the conductivefilm; wherein the low concentration impurity region is overlapped with aportion of the conductive film; wherein at least one selected from thegroup consisting of a source region and a drain region comprises thehigh concentration impurity region; second heating the secondsemiconductor film; irradiating with a first laser light from the firstsurface and with a second laser light from a second surface of thetranslucent substrate to activate the impurity, wherein the second laserlight is a portion of the first laser light which is transmitted throughthe translucent substrate and reflected by a reflector; wherein thereflector is formed adjacent to the second surface of the translucentsubstrate.
 3. A method of manufacturing a semiconductor device, saidmethod comprising the steps of: forming a first semiconductor film overa first surface of a translucent substrate; introducing a metal elementinto the first semiconductor film; first heating the first semiconductorfilm to form a second semiconductor film; forming an insulating film onthe second semiconductor film; forming a conductive film on theinsulating film; introducing an impurity into the second semiconductorfilm to form a channel forming region, at least a low concentrationimpurity region and at least a high concentration impurity region;wherein the channel forming region is overlapped with the conductivefilm; wherein the low concentration impurity region is overlapped with aportion of the conductive film; wherein at least one selected from thegroup consisting of a source region and a drain region comprises thehigh concentration impurity region; second heating the secondsemiconductor film; irradiating with a first laser light from the firstsurface and with a second laser light from a second surface of thetranslucent substrate during third heating the translucent substratefrom the second surface to activate the impurity, wherein the secondlaser light is a portion of the first laser light which is transmittedthrough the translucent substrate and reflected by a reflector; whereinthe reflector is formed adjacent to the second surface of thetranslucent substrate.
 4. A method of manufacturing a semiconductordevice, said method comprising the steps of: forming a firstsemiconductor film over a first surface of a translucent substrate;introducing a metal element into the first semiconductor film; firstheating the first semiconductor film to form a second semiconductorfilm; forming an insulating film on the second semiconductor film;forming a conductive film on the insulating film; introducing animpurity into the second semiconductor film to form a channel formingregion, at least a low concentration impurity region and at least a highconcentration impurity region; wherein the channel forming region isoverlapped with the conductive film; wherein the low concentrationimpurity region is overlapped with a portion of the conductive film;wherein at least one selected from the group consisting of a sourceregion and a drain region comprises the high concentration impurityregion; second heating the second semiconductor film; irradiating with afirst laser light from the first surface in a slant direction withrespect to the translucent substrate and with a second laser light froma second surface of the translucent substrate to activate the impurity,wherein the second laser light is a portion of the first laser lightwhich is transmitted through the translucent substrate and reflected bya reflector; wherein the reflector is formed adjacent to the secondsurface of the translucent substrate.
 5. A method according to claim 1wherein the translucent substrate is heated at a temperature in a rangeof 100-450° C.
 6. A method according to claim 3, wherein the translucentsubstrate is heated at a temperature in a range of 100-450° C. in thethird heating step.
 7. A method according to claim 1, wherein a firstelement comprises at least one selected from the group consisting of He,Ne, Ar, Kr and Xe, wherein a second element comprises at least oneselected from group 15 in the periodic table, and wherein the impuritycomprises at least one selected from the group consisting of the firstand second elements.
 8. A method according to claim 1, wherein a firstelement comprises at least one selected from the group consisting of He,Ne, Ar, Kr and Xe, wherein a second element comprises at least oneselected from group 13 in the periodic table, and wherein the impuritycomprises at least one selected from the group consisting of the firstand second elements.
 9. A method according to claim 1, wherein a firstelement comprises at least one selected from the group consisting of He,Ne, Ar, Kr and Xe, wherein a second element comprises at least oneselected from group 15 in the periodic table, wherein a third elementcomprises at least one selected from group 13 in the periodic table, andwherein the impurity comprises at least one selected from the groupconsisting of the first, second and third elements.
 10. A methodaccording to claim 1, wherein a first element comprises at least oneselected from group 15 in the periodic table, wherein a second elementcomprises at least one selected from group 13 in the periodic table, andwherein the impurity comprises at least one selected from the groupconsisting of the first and second elements.
 11. A method according toclaim 1, wherein the reflector has a curved surface to reflect the firstlaser light.
 12. A method according to claim 1, wherein the reflectorhas rugged portions on a reflecting surface thereof to effect diffusereflection of the first laser light.
 13. A method according to claim 1,wherein each of the first and second laser lights has a wavelength in arange of 300 nm or more.
 14. A method according to claim 1, wherein eachof the first and second laser lights is one selected from the groupconsisting of a pulse oscillation type gas laser, a continuous lightemitting type gas laser, a solid laser and a metallic laser.
 15. Amethod according to claim 1, wherein the semiconductor device is oneselected from the group consisting of an active matrix type liquidcrystal display, an active matrix type EC display and an active matrixtype light emitting display.
 16. A method according to claim 1, whereinthe semiconductor device is one selected from the group consisting of apersonal computer, a video camera, a mobile computer, a goggle typedisplay, a player using a record medium recorded with programs, adigital camera, a front type projector, a rear type projector, aportable telephone, a portable book and a display.
 17. A methodaccording to claim 2, wherein a first element comprises at least oneselected from the group consisting of He, Ne, Ar, Kr and Xe, wherein asecond element comprises at least one selected from group 15 in theperiodic table, and wherein the impurity comprises at least one selectedfrom the group consisting of the first and second elements.
 18. A methodaccording to claim 2, wherein a first element comprises at least oneselected from the group consisting of He, Ne, Ar, Kr and Xe, wherein asecond element comprises at least one selected from group 13 in theperiodic table, and wherein the impurity comprises at least one selectedfrom the group consisting of the first and second elements.
 19. A methodaccording to claim 2, wherein a first element comprises at least oneselected from the group consisting of He, Ne, Ar, Kr and Xe, wherein asecond element comprises at least one selected from group 15 in theperiodic table, wherein a third element comprises at least one selectedfrom group 13 in the periodic table, and wherein the impurity comprisesat least one selected from the group consisting of the first, second andthird elements.
 20. A method according to claim 2, wherein a firstelement comprises at least one selected from group 15 in the periodictable, wherein a second element comprises at least one selected fromgroup 13 in the periodic table, and wherein the impurity comprises atleast one selected from the group consisting of the first and secondelements.
 21. A method according to claim 2, wherein the reflector has acurved surface to reflect the first laser light.
 22. A method accordingto claim 2, wherein the reflector has rugged portions on a reflectingsurface thereof to effect diffuse reflection of the first laser light.23. A method according to claim 2, wherein each of the first and secondlaser lights has a wavelength in a range of 300 nm or more.
 24. A methodaccording to claim 2, wherein each of the first and second laser lightsis one selected from the group consisting of a pulse oscillation typegas laser, a continuous light emitting type gas laser, a solid laser anda metallic laser.
 25. A method according to claim 2, wherein thesemiconductor device is one selected from the group consisting of anactive matrix type liquid crystal display, an active matrix type ECdisplay and an active matrix type light emitting display.
 26. A methodaccording to claim 2, wherein the semiconductor device is one selectedfrom the group consisting of a personal computer, a video camera, amobile computer, a goggle type display, a player using a record mediumrecorded with programs, a digital camera, a front type projector, a reartype projector, a portable telephone, a portable book and a display. 27.A method according to claim 3, wherein a first element comprises atleast one selected from the group consisting of He, Ne, Ar, Kr and Xe,wherein a second element comprises at least one selected from group 15in the periodic table, and wherein the impurity comprises at least oneselected from the group consisting of the first and second elements. 28.A method according to claim 3, wherein a first element comprises atleast one selected from the group consisting of He, Ne, Ar, Kr and Xe,wherein a second element comprises at least one selected from group 13in the periodic table, and wherein the impurity comprises at least oneselected from the group consisting of the first and second elements. 29.A method according to claim 3, wherein a first element comprises atleast one selected from the group consisting of He, Ne, Ar, Kr and Xe,wherein a second element comprises at least one selected from group 15in the periodic table, wherein a third element comprises at least oneselected from group 13 in the periodic table, and wherein the impuritycomprises at least one selected from the group consisting of the first,second and third elements.
 30. A method according to claim 3, wherein afirst element comprises at least one selected from group 15 in theperiodic table, wherein a second element comprises at least one selectedfrom group 13 in the periodic table, and wherein the impurity comprisesat least one selected from the group consisting of the first and secondelements.
 31. A method according to claim 3, wherein the reflector has acurved surface to reflect the first laser light.
 32. A method accordingto claim 3, wherein the reflector has rugged portions on a reflectingsurface thereof to effect diffuse reflection of the first laser light.33. A method according to claim 3, wherein each of the first and secondlaser lights has a wavelength in a range of 300 nm or more.
 34. A methodaccording to claim 3, wherein each of the first and second laser lightsis one selected from the group consisting of a pulse oscillation typegas laser, a continuous light emitting type gas laser, a solid laser anda metallic laser.
 35. A method according to claim 3, wherein the metalelement comprises at least one selected from the group consisting of Fe,Co, Ni, Ru, Rh, Pd, Os, Ir, Pt, Cu, Ag, Au, Sn, and Sh.
 36. A methodaccording to claim 3, wherein the semiconductor device is one selectedfrom the group consisting of an active matrix type liquid crystaldisplay, an active matrix type EC display and an active matrix typelight emitting display.
 37. A method according to claim 3, wherein thesemiconductor device is one selected from the group consisting of apersonal computer, a video camera, a mobile computer, a goggle typedisplay, a player using a record medium recorded with programs, adigital camera, a front type projector, a rear type projector, aportable telephone, a portable book and a display.
 38. A methodaccording to claim 4 wherein a first element comprises at least oneselected from the group consisting of He, Ne, Ar, Kr and Xe, wherein asecond element comprises at least one selected from group 15 in theperiodic table, and wherein the impurity comprises at least one selectedfrom the group consisting of the first and second elements.
 39. A methodaccording to claim 4 wherein a first element comprises at least oneselected from the group consisting of He, Ne, Ar, Kr and Xe, wherein asecond element comprises at least one selected from group 13 in theperiodic table, and wherein the impurity comprises at least one selectedfrom the group consisting of the first and second elements.
 40. A methodaccording to claim 4, wherein a first element comprises at least oneselected from the group consisting of He, Ne, Ar, Kr and Xe, wherein asecond element comprises at least one selected from group 15 in theperiodic table, wherein a third element comprises at least one selectedfrom group 13 in the periodic table, and wherein the impurity comprisesat least one selected from the group consisting of the first, second andthird elements.
 41. A method according to claim 4, wherein a firstelement comprises at least one selected from group 15 in the periodictable, wherein a second element comprises at least one selected fromgroup 13 in the periodic table, and wherein the impurity comprises atleast one selected from the group consisting of the first and secondelements.
 42. A method according to claim 4, wherein the reflector has acurved surface to reflect the first laser light.
 43. A method accordingto claim 4, wherein the reflector has rugged portions on a reflectingsurface thereof to effect diffuse reflection of the first laser light.44. A method according to claim 4, wherein each of the first and secondlaser lights has a wavelength in a range of 300 nm or more.
 45. A methodaccording to claim 4, wherein each of the first and second laser lightsis one selected from the group consisting of a pulse oscillation typegas laser, a continuous light emitting type gas laser, a solid laser anda metallic laser.
 46. A method according to claim 4, wherein the metalelement comprises at least one selected from the group consisting of Fe,Co, Ni, Ru, Rh, Pd, Os, Ir, Pt, Cu, Ag, Au, Sn, and Sb.
 47. A methodaccording to claim 4, wherein the semiconductor device is one selectedfrom the group consisting of an active matrix type liquid crystaldisplay, an active matrix type EC display and an active matrix typelight emitting display.
 48. A method according to claim 4 wherein thesemiconductor device is one selected from the group consisting of apersonal computer, a video camera, a mobile computer, a goggle typedisplay, a player using a record medium recorded with programs, adigital camera, a front type projector, a rear type projector, aportable telephone, a portable book and a display.